THE CYBER FOOT PRINT AND CRIMINAL TRACKING

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At 10:00 a.m. one morning in 1999, an elderly woman in Osaka, Japan, became alarmed. Her 74-year-old husband, who suffers from dementia, had left four hours earlier and had not yet returned. She did not panic, but contacted the provider of her personal locator service, Life Service Center. Within a minute, the provider found him on the second floor of a department store, simply by paging a miniature locator device secured to the man’s clothes. Forty minutes later, when the man’s son arrived at the department store, his father had already left. Fortunately, the service provider continued tracking the elderly man and was able to direct the son to the fourth floor of an Osaka hotel. At 1:10 p.m., the two were reunited. Locus Corp. provided the system that made this possible.

The belief that it should be easy to find anyone, anywhere, at any time with a few pushes of a button has caught on with the advent of the global positioning system (GPS). People imagine a miniature device, attached to one’s person, that reports one’s whereabouts almost instantaneously. Add the highly practical need to find missing persons promptly, and the personal locator system (PLS) industry is born.

Systems of this nature, whether based on the GPS or some other technology, are being tested throughout the world. Some, in fact, are already being deployed in Japan. The service alone can be sold by cellular companies, which base it on their wireless infrastructure. But several companies looking into the technology options plan to offer a broad array of services to the public and to businesses.

In Japan, location services are now commercially available to 74% of the nation’s population, inclu1ding Tokyo, Osaka, Kyoto, Yokohama, Nagasaki, and Hiroshima. Initially designed to support the mentally handicapped, personal locator services have expanded to serve children, the elderly, tourist groups, and security patrols, as well. They may also be used to track valuables and recover stolen vehicles. Not surprisingly, service areas coincide with wireless infrastructure deployments, which personal locators have exploited since their beginning in 1998.

In the United States, two further factors encourage the adoption of these geolocation systems. One is the need to effectively monitor offenders on parole and probation. Tagging offenders with locator devices would tighten their supervision and enhance public safety, and could even reduce the prison population. The other is the wish to provide wireless callers with enhanced 911 (E-911) emergency services. For land-line telephony, the location of a phone from which a 911 call is made appears automatically on the 911 operator’s computer screen. But callers using cellular phones could be anywhere and unlocatable, unless location technology were applied to the wireless telephone system.

Of course, wireless services for locating vehicles have been thwarting car theft and managing fleets of cars since the mid-1980s. But unlike vehicular locators, which are less constrained by size and power, locators borne on the person have to be the size of a pager, and their power output has to be less than 1 W, because they can only carry a small battery that cannot be continuously recharged. Most challenging of all, personal locators have to be able to operate in RF-shielded areas such as buildings, because people spend a lot of their time indoors.

One PLS Architecture

A personal locator system is likely to involve a service provider, a location center, and a wireless network. In this setting, three scenarios, each involving a different operating mode, are possible. The person bearing a locator device is either being sought by a subscriber to the service, or is seeking help from the subscriber, or, as in the case of a parolee, is having his or her whereabouts monitored continuously.

Consider again the introductory example, but from a system architecture perspective. It is representative of the first scenario, based on the paging mode, wherein the person with the locator device is sought. In this instance, the subscriber calls the service provider, giving the operator there a password and the “wanted” person’s identification (user) number (ID). The operator enters the ID into a computer, which transmits it to another computer at the location center. That machine calls the locator device, in effect paging it to establish communication through the PHS wireless telephone switching office (where PHS stands for personal handy phone systems). Immediately the office forwards the call to the wireless base station nearest the locator.

Once communication is established between the center and the device, the center asks the device for the signal strength data and IDs of any base stations in its vicinity. The locator replies, and from those inputs, plus RF database information on the base stations, the center computes the locator’s coordinates. Details of the geolocation technology behind this architecture follow in subheading: “Enhanced Signal Strength.”

These coordinates are transmitted to the service provider’s computer, which displays the missing person’s position on a street map for the service operator to report to the subscriber. The user’s location is continuously updated on the service provider’s map as long as the location center maintains its call connection to the locator device.

In a second scenario, surrounding the emergency mode, the user of the locator is lost or in dire straits of one sort or another, and presses the device’s panic button. The locator calls the location center, which computes the user’s position and alerts the service provider, which in turn alerts the subscriber to the user’s situation.

The system can employ either packet data or voice channel communications. If a data channel is used, the service takes about 8 seconds to obtain a geolocation fix. But if a voice channel is used, the wait could last up to 33 seconds because of processing differences between the two channel types.

Several minutes may be added by communication between the service’s operator and the subscriber. Such a human interface may be necessary given the complexity of Japanese (as explained in the Japanese example earlier) city-addressing schemes. Otherwise, subscribers using personal computers may obtain the information directly from the computer of either the service provider or location center.

Both the emergency and paging operating modes of personal locator systems are characterized as intermittent. In addition, a continuous automatic mode, in which the system polls the locator nonstop, is possible. Strictly speaking, the polling is periodic rather than continuous, but the latter term is more common.

Of the three locator modes, this last requires the most RF bandwidth and battery power. If it were implemented with a continuous voice call between the system and the locator, the expense would be beyond the reach of most applications. Assuming a minimal cost of 4 cents per minute for airtime, such a connection would cost US $57.60 a day—and also drain the locator battery within a few hours.

Packet data calls between the locator and the rest of the system are far more economical. In the packet version, the locator is likely to be polled every few minutes, exchanging 100 bytes or so with the system in a fraction of a second.

Given a 3-minute polling interval and a 1-cent-per-poll cost, the daily cost per locator would be only $4.80.

Note 

For most of the time, the locator would be in standby mode, conserving valuable battery charge. Another plus, upcoming third-generation mobile wireless telephony will increase the availability of packet data communications.

Six Technologies

A personal locator system could use any of several technologies. Among the most common methods are angle and time difference of the signal’s arrival, global positioning system (GPS) and the more recent assisted GPS, enhanced signal strength, and location fingerprinting.

Signal Direction

The simplest is based on measuring the direction of a signal received from an RF transmitter at a single point. This can be done by pointing a directional antenna along the line of maximum signal strength. Alternatively, signal direction can be determined from the difference in time of arrival of the incoming signals at different elements of the antenna. A two-element antenna is typically used to cover angles of ±60 degrees. To achieve 360-degree coverage, a six-element antenna can be used.

A single mobile directional antenna can give only the bearing, not the position, of a transmitting object. The single bearing can be combined with other information, such as terrain data, to provide location. Such an antenna is generally used to approach and locate objects up to several kilometers away. A common use of this technique is tracking RF-tagged wildlife. The same basic technique is used by LoJack Corp., of Dedham, Massachusetts, in its system for finding stolen vehicles.

With two directional antennas spaced well apart, however, the position of a transmitting device in a plane can be computed. In this method, also known as the angle of arrival (AOA) method, transmitter position is determined from the known (fixed) position of the receivers’ antennas and the angle of arrival of the signals with respect to the antennas.

Angle measurement precision affects the accuracy of positioning calculations, as does the geometry of the transmitting device and receiving antennas. For example, if a transmitter is too near a line drawn between two receiving antennas, its measured position could be off by more than the distance between the antennas. Fortunately, multiple receiver antennas distributed throughout the area of coverage enable the cellular system to select those antennas that introduce the smallest error.

Signal Times Of Arrival

Similarly, the time difference of arrival (TDOA) between signals received at the geographically disparate antennas can be used to determine position. Given the speed of light and known transmit and receive times, the distance between the mobile locator and receiver antenna can be calculated.

Accurate clocks are of the essence here, because an error of 1 µs in time corresponds to an error of 300 meters in space. Also, all clocks used must be synchronized. But as synchronizing the mobile locator clock is usually impractical, at least three receiving antennas are required for the calculation.

Sometimes the calculations produce ambiguous results, which can be resolved by considering signals received at a fourth antenna. As with the angle of arrival method, the relative positions of receivers and transmitter affect computational errors.

In an alternative time difference scheme, the locator and the antennas reverse roles: the antennas are transmitters and the mobile locator is a receiver. This technique is known as forward link trilateration (FLT). This is relatively simple to implement in some code-division multiple access (CDMA) wireless systems, where the time difference of arrival can be determined from the phase difference between pseudo-random noise code sequences of 0s and 1s transmitted from two antennas.

Global Positioning System

As previously explained, a global positioning system (GPS) relies on a constellation of 24 satellites. It, too, employs signal timing to determine position, but the mobile locator is a receiver and the orbiting satellites are transmitters. The satellites transmit spread-spectrum signals on two frequency bands denoted L₁ (1575.42 MHz) and L₂ (1223.6 MHz). The signals are modulated by two pseudo-random noise codes, the precision (P) code, and coarse/acquisition (C/A) code. The GPS signal is further modulated with a data message known as the GPS navigation message.

Note 

Only the C/A code in the L₁ band is used in civilian applications and, hence, is of interest here.

To acquire the satellites’ signals, the GPS receiver generates a replica of the satellites’ pseudo-random noise codes. The GPS navigation message can be demodulated only if the replica can be matched and synchronized with the pseudo-random noise codes received. If the receiver cannot match and synchronize its replica, the GPS signal appears to the receiver as noise. Matching the pseudo-random noise codes and using the satellites’ navigation message also enables the receiver to calculate the signal transmit time as well as the coordinates of the satellites.

The accuracy of GPS position calculations depends partly on measurement accuracy and partly on satellite configuration. Measurement errors depend on physical parameters, such as ionospheric delays and orbital uncertainties, and on the selective availability (SA) factor, introduced by the U.S. Department of Defense to degrade satellite data for nonmilitary users. Total measurement errors are estimated at 35 meters; without selective availability, they are reduced to 8 meters.

The configuration of the GPS satellites at the time of the measurements adds further distortion. If those in sight are scattered throughout the sky, the measurement error is multiplied by about 1.5. If they are clustered together, the multiplier is 5 or more.

To estimate actual position accuracy, it is necessary to combine the measurement errors with the errors introduced by the spatial disposition of the satellites. To determine its position, a GPS receiver calculates its x, y, and z coordinates as well as the time the satellite signals arrive. Data must be acquired from at least four (and preferably more) observable GPS satellites. When fewer than four satellites are in view, in areas such as city canyons, one remedy is a hybrid approach, augmenting GPS with the land-based measurements called “forward link trilateration.” To illustrate, the use of two GPS satellites and two cellular base stations would suffice to determine a locator’s position.

The unobstructed line of sight to the orbiting transmitters is important. The satellite signals are weak (below 10^-15 W) when they arrive at a receiver’s antenna, and are further weakened upon entering a building. Moreover, a conventional GPS receiver could take several minutes to acquire the satellite signals and, therefore, tends to operate continuously rather than be turned on and off for each acquisition. The drain on the receiver’s battery is significant.

Server-Assisted GPS

To combat the shortcomings of GPS, an innovative technique known as “server-assisted GPS” was introduced in 1998. The idea is to place stationary servers throughout the area of coverage to assist mobile receivers to acquire the GPS signals. In effect, the servers are stationary GPS receivers that enhance the mobile GPS receiver’s capabilities by helping to carry their weak signals from satellites to locator. The server includes a radio interface, for communicating with the mobile GPS receiver, and its own stationary GPS receiver, whose antenna has full view of the sky and monitors signals continuously from all the satellites within view.

To ask a mobile GPS receiver for its position, the server feeds it satellite information through the radio interface. Included in this information is a list of observable GPS satellites and other data that enable the mobile receiver to synchronize and match its pseudo-random noise code replicas with those of the satellites. Within about a second, the GPS receiver collects sufficient information for geolocation computation and sends the data back to the server. The server can then combine this information with data from the satellites’ navigation message to determine the position of the mobile device.

With the assisted GPS approach, the mobile receivers conserve power by not continuously tracking the satellites’ signals. Moreover, they have only to track the pseudo-random noise code and not extract the satellites’ navigation message from the signal, in effect, becoming sensitive enough to acquire GPS signals inside most buildings.

In addition, the assisted version of the technology attains greater accuracy. Because the actual position of the stationary GPS receiver is known, the difference between that and its measured position can be used to calculate a correction to the mobile receiver’s position. In other words, assisted GPS is inherently differential GPS (DGPS), which counters some of the inaccuracy in civilian GPS service.

Note 

The most accurate GPS service is reserved for military use.

In June of 2000, Lucent Technologies Inc., of Murray Hill, New Jersey, announced that its wireless assisted GPS had attained an accuracy of better than 5 meters outdoors—an achievement attributable to the differential GPS capability of assisted GPS. More good news in this field was announced by SiRF Technology Inc., of Santa Clara, California, in the form of a postage-stamp-sized chipset (Star II) with built-in DGPS. In addition to providing improved GPS capability, it also offers reduced power consumption and greater accuracy, as well as performing well at handling weak signals.

Enhanced Signal Strength

If no obstructions are present, computing the position of a mobile locator is straightforward for both the signal timing and signal strength methods. When timing is used, the speed of light is multiplied by the time a signal takes to propagate between the two points gives the distance between them.

For the signal strength method, the distance between two points can be determined from the signal attenuation between the points. However, direct line contact seldom exists inside buildings, where signal attenuation is usually unknown and many indirect paths between transmitter and receiver are likely. Although techniques exist for reducing this multipath effect, the effect cannot be eliminated, and the errors it produces are difficult to predict. Multipath effects impede signal timing methods somewhat, but affect signal strength methods even more.

In addition, signal strength is very sensitive to antenna orientation, attenuation by obstructions, and other operating conditions. In contrast, signal timing is unaffected by antenna orientation and is less sensitive to attenuation.

Nonetheless, an enhanced signal strength (ESS) method that overcomes such impediments as multipath effects, attenuation, and antenna orientation has allowed the deployment of personal locator systems in PHS service areas in Japan. Such a system takes in three-dimensional information on the lay of the land, buildings, elevated highways, railroads, and other obstructions, and uses it to simulate the RF signal propagation characteristics of every PHS wireless transmitting antenna in the area of interest. The location system center stores the results in an RF database.

The position of a mobile locator is determined by getting it to measure the signal strength of preferably three to five base stations. From this input plus information from the base stations’ databases, the system can calculate the position of the locator. The mean accuracy of the ESS is 40–50 meters. Inside large public buildings, with a PHS base station on every floor, the system can indicate a specific floor level. In subway and railroad stations, the availability of base stations makes it possible to find an individual on a specific track.

The stand-alone locator used by Locus Corp.’s enhanced signal strength method weighs only 58 grams and can operate for 16 days on a single battery charge. The ESS geolocation capabilities are also available in a standard PHS phone handset, in which the firmware has been modified. Presently, researchers in Japan are investigating how to apply ESS technology to other wireless phone systems.

Location Fingerprinting

Instead of exploiting signal timing or signal strength, a new technique from U.S. Wireless Corp., of San Ramon, California, relies on signal structure characteristics. Called “location fingerprinting,” it turns the multipath phenomenon to surprisingly good use: By combining the multipath pattern with other signal characteristics, it creates a signature unique to a given location.

U.S. Wireless’s proprietary RadioCamera system includes a signal signature database of a location grid for a specific service area. To generate this database, a vehicle drives through the coverage area transmitting signals to a monitoring site. The system analyzes the incoming signals, compiles a unique signature for each square in the location grid, and stores it in the database. Neighboring grid points are spaced about 30 meters apart.

To determine the position of a mobile transmitter, the RadioCamera system matches the transmitter’s signal signature to an entry in the database. Multipoint signal reception is not required, although it is highly desirable. The system can use data from only a single point to determine location. Moving traffic, including vehicles, animals, and/or people, and changes in foliage or weather do not affect the system’s capabilities.

What’s PLS Good For?

In the United States, the need to provide wireless phone users with emergency 911 services has been one of the spurs to the development of location technologies. Today, an enhanced 911 (E-911) emergency call made over a land line is routed to a public safety answering point (PSAP), which matches the caller’s number to an entry in an automatic location information database. When the match is made, this database provides the PSAP with the street address plus a location in a building—maybe the floor or office of the caller handset. So quickly is the caller located that the emergency crew can respond within 5 to 7 minutes on average.

But the very mobility of wireless handsets rules out a simple database relationship between phone number and location. In fact, the response to a wireless call can be 10 times longer than for a land-line call—far from ideal in an emergency.

Accordingly, the U.S. Federal Communications Commission (FCC) in Washington, D.C., directed operators of wireless phone services to enable their E-911 services to locate callers. The directive specified two phases. The first required an accuracy of several kilometers by April 1998 and the second required an accuracy of 125 meters with 0.67 probability by 2002. Whereas the first phase needed only software changes to the system, the second required the adoption of new location technologies.

The original FCC directive for Phase II also required support for existing handsets, which implied that only network upgrades would be acceptable. Yet a network-only solution would preclude the use of emerging technologies, such as assisted GPS, because that would require handset modification in addition to any network infrastructure and software changes. All users might not bring in their handsets for modification, severely complicating support for handsets already in service.

To ease the introduction of new technologies, in September 1999, the FCC modified its original Phase II directive to permit handset-enabled solutions and also to tighten the accuracy required. In addition to the many technical roadblocks to implementing the E-911 directive, an even greater obstacle is cost. Upgrading all the wireless networks will cost billions of dollars. Cost recovery is the central issue for cellular service providers. Although wireless subscribers are the most likely source of recouping the cost, the government has made no formal decisions yet.

Presently, only the U.S. government requires its wireless companies to add caller geolocation to their E-911 services. But as the United States is a major telecommunications market, many manufacturers of wireless telecommunications equipment elsewhere are developing approaches to meet the commission’s directive.

In an international development, a working group of the European Telecommunications Standards Institute (ETSI), based in Sophia Antipolis, France, is currently drafting a standard for supporting location services for the Global System for Mobile Communications (GSM). Currently, GSM is the most common mobile wireless system in the world and is available in more countries than any other wireless system.

Monitoring Tops Services LIST

Wireless E-911 just helps the individual. But monitoring the mentally impaired and criminals could have even greater impacts on society at large. With the changing demographics of the developed world, the percentage of individuals over age 65 will soar over the next several decades. So will the number of elderly afflicted with age-related mental impairments. Most of the five million or so U.S. patients diagnosed with Alzheimer’s disease are over age 65.

Recall how personal locator technology helped a family find a mentally impaired elderly man, fortunately within 50 minutes or so. But what if many hours passed before anyone noticed that the man was missing? What if he had run into some kind of difficulty during that time? Being mentally impaired, he would be unlikely to press the panic button. An automatic polling system could solve this problem by checking whether the man was within a defined polygonal area or not—the location service and the family would be alerted whenever the man went out of this area.

As the population ages, the need for and cost of long-term care are likely to increase, too. Today it costs over $40,000 per year in the United States to care for a patient in a nursing home. Systems that monitor the whereabouts of the mentally impaired elderly could help them live longer in their communities and spend less time in institutions.

Criminal justice is another area of social concern where personal locators could intervene. The United States leads industrial nations in the percentage of its population incarcerated. In 2000, according to U.S. Department of Justice statistics, almost 5.2 million people were serving time in U.S. jails and prisons, and a further 8 million were in parole and probation programs. In comparison, in Japan in 2000, only 135,000 were serving prison terms while 180,000 were on parole or probation.

The high human and monetary cost of corrections could be cut by new technologies, such as personal locator systems, that would reduce prison populations and improve the monitoring of parolees and persons on probation. First-generation monitoring systems, introduced in the mid-1980s, track the location of the offen-der in a very confined area, such as the home. They enable the corrections system to verify that a parolee stays there during specified periods, 6 p.m. to 6 a.m., say.

But by day, when the offender is presumably at work, these systems can do nothing.

Second-generation monitoring systems do better. A tamperproof personal locator is fastened on the offender and tracked continuously and automatically over a wide area. The newer system compares the actual with the supposed positions of the offender, as stored in a database. If any violation or tampering with the locator occurs, the system alerts the appropriate corrections or law enforcement agencies.

The goal is to verify that parolees and probationers comply with the directives imposed by the corrections system as to where and when they should and should not be by day and night. For example, a child molester is excluded from school areas, and a stalker is excluded from areas near the home and workplace of the victim.

Storage of the offender’s ongoing whereabouts in an electronic file benefits law enforcement agencies in other ways.^[v] The record can be used to exclude or include a monitored offender as a suspect in a crime by comparing events at the crime scene with the file entries.

In 1996, two companies, Advanced Business Sciences Inc. (ABS) of Omaha, Nebraska (http://www.abscomtrak.com), and Pro Tech Monitoring Inc., located in Palm Harbor, Florida (http://www.ptm.com), were the first to introduce GPS-based continuous monitoring systems for criminal offenders. These systems are deployed in, among other places, Michigan, Minnesota, Florida, Colorado, Wisconsin, Pennsylvania, South Carolina, Arizona, Ohio, Texas, and Nebraska. More recently, BI Inc., headquartered in Boulder, Colorado (http://www.bi.com), the leading manufacturer of first-generation offender monitoring systems, began testing its version of a GPS-based system.

The Pro Tech Monitoring, ABS, and BI systems all include a personal locator, a wireless telephone interface, and a location center. The personal locator has two parts, a GPS unit and an ankle bracelet. The ankle bracelet, which employs tamper-detection circuitry, uses a low-power transmitter with a range of about 50 meters. The GPS unit consists of a GPS receiver, a wireless phone component, and a receiver to detect the bracelet signal. The offender carries the GPS unit by hand, or in the case of the ABS system, wears it on a belt.

Should the GPS unit fail to detect the bracelet signal (probably because it is out of range) or should the bracelet circuitry detect tampering, the unit will alert the location center through its wireless interface. What’s more, the unit monitors its own position by means of its GPS receiver whenever the satellite signals are detectable, primarily outdoors.

The GPS unit can operate in either of two modes: autonomous or continuous. In autonomous mode, it logs the offender’s location in its internal memory. It compares this position with an on-board database of exclusion and inclusion zones for the offender. When it detects a zone or other violation, it alerts the location center with a wireless call. In this mode, once or twice a day the GPS unit dials the location center and updates it with the logged data.

Operation in autonomous mode, of course, avoids the costly continuous voice-type wireless connections. Using the far less expensive, packet-based, cellular digital packet data (CDPD) wireless phone connection, the GPS unit can maintain continuous real-time contact with the location center—the second operating mode. Unfortunately, however, CDPD is unavailable in many areas.

Splitting the locator in two (into a bracelet and GPS unit) offers a simple recharging strategy. The unit’s batteries usually require a daily recharging to power the GPS unit. At night, when the offender is typically required to be at home, the unit is placed in a docking station for recharging, while maintaining contact with the location center all the while and sending information whenever appropriate.

Privacy, Security Still Issues

Confidentiality of information about a person’s whereabouts is a serious concern for location technology. Databases already store large amounts of personal information, including medical data, marketing preferences, and credit information. Lax security could lead to serious abuse of this data. Access to a database of location information could aggravate this situation by further exposing a person’s movements. Moreover, it can have real-time implications. For example, someone could find and harm a victim.

The location information stored in databases needs to be secured, as does the tracking and locating process itself. Because RF communications are used, eavesdropping is a possibility. To reduce this risk, location information can be encrypted or transmitted using coded signals employing such spread-spectrum technology as CDMA.

Privacy protection can also depend on the technology used. For example, in GPS or the enhanced-signal-strength method, the location system uses information captured and transmitted by the locator. Some devices are equipped with an option to block such transmissions, preventing the system from locating the device. But in network-based locator systems that measure the locator’s signal characteristics without requiring its cooperation, the only safe way for users to keep their locations secret is to turn off the device.

More Work To Be Done

Despite the strides made in recent years in personal locator technologies, much work remains to be done on their accuracy, locator miniaturization, battery life, multipath effects, ability to penetrate buildings, and the economical use of RF bandwidth. In addition, hybrid systems may be required to provide improved coverage and open the door to new applications.

Reducing the cost of deploying location technology is essential in removing barriers to the use of location services. The concern over how to pay for E-911 services demonstrates the need for cost reduction. However, if a rich set of location services could share the expense of the additional infrastructure needed to support these services, the cost per subscriber would be reduced. The new location technologies, as well as wireless data packet services that are now emerging around the globe, offer opportunities for entrepreneurs to expand personal locator services.

In June 1999, Loc8.net (http://www.loc8.net), based in Seattle, Washington, announced that in late 2002 it intends to provide location-based services employing the ReFLEX two-way paging wireless infrastructure. The services, which will use wireless assisted GPS, will include personal locator services for Alzheimer patients and children, as well as commercial services such as fleet management. The two-way paging systems using ReFLEX, developed by Motorola Inc. of Schaumberg, Illinois, cover 95% of the U.S. population. The Loc8.net system operates in emergency and paging modes.

Recent advances such as assisted GPS are likely to enhance GPS-based offender-monitoring systems, reducing device size and power consumption, adding to accuracy, and offering new capabilities such as in-building tracking. In the future, personal locators could bring many other blessings. Equipping young children with personal locators may offer parents greater peace of mind. Small enough locators could even track pets.

Personal locators could also be helpful to medical patients where the locator would be combined with a detector that monitors the patient’s vital signs. If the detector picked up abnormalities in the signals, it would alert the nurse or physician with both medical and location information. Such a service could offer a patient greater freedom and a shorter stay in hospital or nursing home. Its greatest contribution, however, may be peace of mind for patients, their families, and doctors.

Obviously, technical and commercial considerations will determine the success of the technology. Issues of users’ privacy and confidentiality will, however, have to be addressed first.

^[v]John R. Vacca, The Essential Guide to Storage Area Networks, Prentice Hall, 2002.

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