Doing some research on personal locator GPS systems such as those that might be used for tracking children or Alzheimer's subjects.
- AI to assist Alzheimer's patients - Wired News June 24, 2002
- Wherify Wireless Location Service uses a GPSr and cellular transmitter to provide position information.
- A satellite baby-sitting service - Wired News May 2, 2002
Contains the statement that Applied Digital plans to develop an implantable GPS within 8 months. Nearly three years later their website has no info about such a device.
- ProTech active offender tracking system. Uses cellular/wireless to report position of the base unit.
- Anatomy of a spam Wired article tracks down the info on the "miracle" product Kid Track. Describes some of the problems with such a system.
Assesment: There are two problems with tracking kids and Alzheimer's patients. One is finding out where they are and the other is getting that information to the right place to do something with it. The first problem is not terribly difficult. Micro-GPS receivers have become commonplace and should have the accuracy needed to get a searcher close enough to a subject for a find.
Personal locator beacons, as are their predecessors, emergency location transmitters, are designed for locating the transmitter. Both technologies, however, depend on being triggered, in the case of PLB's by deliberate action on the part of the subject. Perhaps it would be possible to have a device that could be triggered by a radio signal instead of manually. Similar to General Motor's On-Star system a signal sent from the satellite would cause the beacon to go into transmit mode. The transmission could include either a directional RF signal or an encoded data signal with GPS location.
The PLB/ELT satellite network is the only network of its type in existence. Creating such a network would be very expensive and likely require years to complete. The network also depends heavily on ground stations, staff and computer power to make the network work.
A more plausible solution would be some kind of remote trigger. Cellular networks provide a convenient trigger in many locations as the existing infrastructure is substantial and inexpensive. However, there are many locations where people want to go that don't have cellular coverage. A two-transmitter system may be the best solution. Similar to the offender tracking system above, a parent unit transmits to the child's unit. Upon receiving a signal the child unit is reset and does not transmit for another 30 minutes. If the child's unit is allowed to go 30 minutes without an 'off' signal from the parent unit it switches to transmit mode. Transmit would intermittently send a signal that could be used to locate the subject. A kinetic power supply would be ideal if it can generate enough power to transmit.