As someone that is actually in the GPS and child protection business, I can tell you a fair amount about the systems.
first, what you are looking for is actually A-GPS technology, or "Assisted" GPS. The device will attempt to acquire it's position via GPS positioning. This requires a view of the sky, the more open the better. Some devices will be able to acquire a GPS fix from inside a building, but the quality of the signal will be much less and therefore the accuracy will suffer. Typically, you will have accuracy within 3 meters, but that can vary up to 50 meters depending on environmental factors.
The "assisted" part is that the GPS device then uses cellular technology to broadcast it's position back to a server, which in turn then displays the information via a web portal. Obviously the device therefore also has to be within a cellular coverage area (most GPS devices on the market today utilize TMobile for a cellular provider, we are preparing to switch to AT&T for a much better coverage area).
Additionally, since the devices are using cellular networks already, they have the ability to GSM location on top of the GPS location. This helps eliminate the issue of no coverage indoors, but most devices on the market today do not have this feature enabled.
Then most device providers also offer additional services via their web portal when you access the tracking (though some companies try to charge more for these services). You can do things such as geofencing (you may want to find a provider offering polygonal geofencing, as radial geofences can wind up encompassing a vast area that is really outside of the safe zone you are trying to create), breadcrumbing, speed warnings, etc...
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As someone that is actually in the GPS and child protection business, I can tell you a fair amount about the systems. first, what you are looking for is actually A-GPS technology, or "Assisted" GPS. The device will attempt to acquire it's position via GPS positioning. This requires a view of the sky, the more open the better. Some devices will be able to acquire a GPS fix from inside a building, but the quality of the signal will be much less and therefore the accuracy will suffer. Typically, you will have accuracy within 3 meters, but that can vary up to 50 meters depending on environmental factors. The "assisted" part is that the GPS device then uses cellular technology to broadcast it's position back to a server, which in turn then displays the information via a web portal. Obviously the device therefore also has to be within a cellular coverage area (most GPS devices on the market today utilize TMobile for a cellular provider, we are preparing to switch to AT&T for a much better coverage area). Additionally, since the devices are using cellular networks already, they have the ability to GSM location on top of the GPS location. This helps eliminate the issue of no coverage indoors, but most devices on the market today do not have this feature enabled. Then most device providers also offer additional services via their web portal when you access the tracking (though some companies try to charge more for these services). You can do things such as geofencing (you may want to find a provider offering polygonal geofencing, as radial geofences can wind up encompassing a vast area that is really outside of the safe zone you are trying to create), breadcrumbing, speed warnings, etc...