Secure-A-Key is an anti-theft device specifically designed for preventing Keyless Entry theft (relay attacks). The most common way for thieves to steal Keyless GO cars is by using a device to capture the frequency of the vehicle's remote-control key fob, then transmit the data to your vehicle, this will allow the thieves to unlock your vehicle, start the engine and drive it away. 

The Secure-A-Key device for Ford installs inside your vehicle’s Keyless-GO remote control and electronically disables the battery of the remote control after a few minutes of in-activity (no movement of the remote). The remote-control remains disabled until it is moved, then all functions of the remote-control are reactivated.