Mini motion sensor (tilt sensor) to activate/deactivate a 12 volt system.

Hi,
I'm needing a very small and inexpensive motion sensor(tilt sensor) . The sensor will be used to power on/off a 12v relay which activates a device as long as there is any slight movement. When idle the motion sensor cuts the power to the relay. The sensor will be used inside a closed container with a 14.4V battery pack that operates the relay and a small motor.

Many Thanks