GPS tracking explained(2)

Different possibilities to obtain the position information
1) The modem can be programmed as a mobile phone with its own phone number, capable of sending SMS short text messages. If you call the modem‘s phone number, using your own mobile phone, the device answers your call with a SMS message with the co-ordinates of its position. Advantage: you do not need a service contract and you do not have to pay a monthly fee. No-one even needs to know that you use this possibility. Disadvantage: you will have to translate the co-ordinates in the SMS messages to something more meaningful, i.e. a position on a map.

2) The modem can be programmed with your mobile phone number and send you a SMS message with its position every x minutes or hours. The interval can often be changed "over the air" by calling the modem and change some settings. Advantage: same as above. Disadvantage: same as above.

3) With the appropriate software and maps installed on your mobile phone, the SMS messages can be translated to positions on a map on your mobile phone screen. Advantage: same as above. Disadvantage: you need to buy the software and the maps.

4) The modem sends the position information in timely intervals to a server that displays the actual, as well as the past positions, on a map that can be viewed on any computer or mobile phone with Internet access. Advantages: you can follow the GPS tracking device from anywhere in the world. Disadvantages: you need a subscription to a service that delivers these possibilities. Normally you pay a monthly fee for this. The modem also needs an "always-on" connection with the cellular network for which you will have to pay another monthly fee.

5) As more and more mobile phones nowadays are equipped with a GPS receiver, these phones can perfectly be used as GPS tracking devices. There are already many services available for this purpose.

And when there is no cell phone coverage?
Great surfaces of our planet are covered by cell phone towers. But most surfaces are not. We only have to think of the oceans and the deserts. Even in these regions GPS tracking can be done, but the cell phone modem has to be replaced by a satellite modem. This way the position information can be sent over a communication satellite network (not the GPS satellites!). Advantage: In principle these kind of GPS tracking devices can operate everywhere. Disadvantages: These devices are more sophisticated and bigger than GPS tracking devices with a cell phone modem. The devices AND the service are much more expensive.

Can these GPS tracking devices be implanted in humans or pets?
Not today, not tomorrow and not for many years to come. Why? There are two main reasons. The first reason: both the GPS receiver and the cell phone modem need a minimum antenna surface, which is dictated by physical laws. Second, and more important, both devices do consume a great amount of power. This means that they need bulky and heavy rechargeable batteries. Smaller than a small cell phone or a pacemaker they can not be built. And where do you want the electrical connector for recharging the batteries during the night?