Vehicle Tracking Device...

A normal GPS used for navigation such as the Drivesmart you mentioned does not have any transmitting capabilities, and can only receive a signal from the GPS satellites orbiting the earth. 

The GPS receiver gets a signal from each GPS satellite. The satellites transmit the exact time the signals are sent. By subtracting the time the signal was transmitted from the time it was received, the GPS can tell how far it is from each satellite. The GPS receiver also knows the exact position in the sky of the satellites, at the moment they sent their signals. So given the travel time of the GPS signals from three satellites and their exact position in the sky, the GPS receiver can determine your position in three dimensions - east, north and altitude.

There is a complication. To calculate the time the GPS signals took to arrive, the GPS receiver needs to know the time very accurately. The GPS satellites have atomic clocks that keep very precise time, but it's not feasible to equip a GPS receiver with an atomic clock. However, if the GPS receiver uses the signal from a fourth satellite it can solve an equation that lets it determine the exact time, without needing an atomic clock.

Okay, many thanks for that explanation. I think that I understand it a little better now. The Garmin Drivesmart is a receiver only that uses triangulation from multiple satellites to compute vehicle global position and speed. And these satellites are in a geosynchronous orbit with the earth?

So if I needed a tracking device, there would need to be an independent GPS receiver installed in my car that would also be a transmitter in order to send the computed data back to a home computer. A Garmin Drivesmart is a receiver only. A vehicle tracking device would need to be a GPS receiver and a transmitter. Am I understanding this correctly now???  

2465164 said:

A vehicle tracking device would need to be a GPS receiver and a transmitter. Am I understanding this correctly now???

Yes.