The accuracy and reliability of a GPS unit depends on its ability to receive signals from a number of GPS satellites. The GPS unit must have a clear, unobstructed view of the satellites at all times. If this view is obstructed, a GPS receiver is unable to receive or transmit signals and is essentially disabled. Although it sounds like a crazy, tin foil hat joke, a single layer of consumer metal foil can fool any GPS tracking device.
Locate your car or tracker's GPS antenna and receiver.
Wrap the antenna, receiver and wires in regular, store-bought aluminium foil. While one layer of standard 0.2mm aluminium foil should be enough to block radio signals, use two layers to be certain.
Wrap a layer of duct tape around the aluminium foil wrapping to keep it in place. If the GPS antenna and receiver are in a place that will see a lot of wind when the car is in motion, secure the wrapping in place by taping it to another, stationary object.
For those looking to purchase a commercial solution that is easy to turn on and off, there are a number of GPS jamming systems that plug into cigarette lighters.
Some state laws ban the tampering with or jamming of GPS tracking systems.