If the Gps is a real time unit that transmits its location, then you can detect it with any standard bug detector. The problem comes when the GPS is a passive record only type. This is the type that needs to be removed and downloaded to a computer to find where the unit "has been".
I have been trying to find a way to detect there passive units and have not been successful.
GPS transmitors are used to detect the slow movement of the tectonic plates.
Purchase a GPS/GSM detector...they are cheap and easy to operate. The detector will send out a visual flashing lite or audible sound when the detector is near a tracking device. Look in the cars Wheel Wells (all)...Under Front Bumper...Inside Engine Compartment...Under Car...Back Bumper...etc. The best way to find the hidden GPS device on your car is to follow the Battery Wires on your car to detect GPS signals. The GPS unit needs electrical power to operate. Good Luck and Happy Hunting
The WAAS systems improves the accuracy, integrity, and availability in a GPS system.The WAAS specification requires the system detect errors in the GPS
If it is your car no, the GPS is also yours to do with as you wish.
Buy a GPS tracker and set it into car
MOTOsafety GPS Tracker
If you are shopping around for a GPS device, it is an excellent idea to conduct a car GPS comparison before you make a decision on a GPS device purchase. By performing a car GPS comparison, you can identify the key features in each GPS device and compare them against the other GPS devices. When you do this comparison, it is often easy to see which of the many GPS devices is best for you.
Satellites orbiting around earth send information to the GPS , so they detect the change & fix it in their memory.
Most car alarms include GPS tracking.
Portable GPS units work anywhere, in any car or handheld. A factory installed GPS unit generally cannot be moved to another car.
There are many types of car GPS to use in cars with different, specific features that are bound to suit your needs. Check out these reviews on the website, http://reviews.cnet.com/best-GPS/, where they list the top five car GPS.
An in-dash gps system would be better in a car. Handheld gps systems seem to generally have smaller screens and are made specifically for outdoor use. An in-dash gps is designed for in car use.