Writes the Economist: “The new generation of tracking devices combines two existing technologies. One is a global-positioning-system (GPS) chip, which uses radio signals from a network of satellites to work out where it is on the earth’s surface to within a few metres. The other is a mobile-telephone chip, which broadcasts that location to whoever needs to know it. The result is a pocket-sized, or even wrist-sized, personal locator.”
There is a more detailed explanation about the technology offered by ADS:
Applied Digital Solutions (ADS), of Palm Beach, Florida, calls its version of the technology a digital angel. The angel comes in two versions. People get a pager-like device that clips on to their clothing. Animals get a collar.
The angel is intended to look after old people who have become forgetful and young children who have become too adventurous, as well as dogs who are too interested in the bitch next door. The wearer’s guardians define a perimeter beyond which they feel their charge should not wander, and receive alerts via mobile phone or pager when he has gone beyond these boundaries.
The digital angel can also issue an alert when its wearer has fallen down, or when there has been an unexpected change in local temperature of the sort that might be caused, say, by someone falling into a pond. For that to happen, the wearer needs to sport a specially modified wristwatch which has suitable sensors and a wireless link to the pager. Moreover, ADS claims to be on the verge of introducing a version of the watch that can collect and broadcast medical data such as pulse rate, blood pressure, body temperature, electrocardiogram readings and even blood chemistry.
ADS’s device is a type of radio-frequency identification (RFID) chip. Such chips are already implanted into animals to act as pet passports, identifying beasts that do not need to go into quarantine when they cross frontiers. When an RFID chip is interrogated by a reading machine operating at the right radio frequency, its antenna picks up a small amount of energy from the signal. This is used to power the chip. The device then broadcasts data in the chip back to the reader.