Abstract: The present invention is a vehicle or trailer anti-theft device including electro-mechanical means and a temporary electrical power supply. The temporary electrical power supply acts momentarily upon the electro-mechanical device, thereby causing it to move into an activated condition. In its activated condition, it acts upon either on at least one wheel of the trailer, or the vehicle's parking brake system, to lock the at least one wheel, and remains in its activated condition without the need for any external power supply until such time as the electro-mechanical device is activated or re-connected to the temporary electrical power supply whereby the power supply is able to act momentarily upon the electro-mechanical device, and return said device to its deactivated condition, thereby causing the at least one wheel to be unlocked or the vehicle park brake to deactivate.