How to get the position of a Realtime GPS/GSM/GPRS/SMS tracker with google link via Request

I want to track down a vehicle using a GPS tracker. I'm been seeking for a tracker, and I found some GPS/GSM/GPRS/SMS trackers. What I want is to get the GPS tracker position making a single request or have the GPS tracker making requests to some API. Do I have to buy any special device? What Shall I do????