[tghw]

It would seem a much simpler solution would be feasible. A small GSM device that is essentially powered off until it is needed, at which time it would be booted up and begin sending GPS coordinates via SMS. If you wanted higher reliability, you could look into the FM-based system that LoJack uses, but either way, constant communication seems unnecessary.

[jacalulu]

Great points, this is something that we have given a lot of thought towards. We are going to be pinging the device at certain points (when someone logs into the portal for example), and the device will also send data at set intervals (we can adjust how often we send data to save battery life, and based on a few other things). When the device is not actively sending data or establishing a connected we do sleep the device.

We opted not to send GPS location via SMS because it is a lot less secure. We are also sending more than just GPS data, all of which we would have to interpret on the server side anyways thus complicating the implementation. We looked into this and for a variety of reasons it made more sense to use data to transmit information from the device.

[tghw]

Doesn't that place a pretty large assumption on good data coverage? I live in Denver, which generally has good coverage, but my last place was in a total dead zone and I had to get a microcell device to be able to use the phone indoors. SMS almost always got through, OTOH.

[wesley]

Is there anything like this out there already? With good battery life.

[robg]

They use base stations. Here's one:

http://www.qmedichealth.com/