A lockdown device for a power tool includes a housing containing a battery, a processor, and a relay. The housing mounts to an aperture in a power tool so as to be locked thereto and so as to be immovable therefrom without dismantling of the power tool. An electrical power cord mounts to the housing in electrical communication with the processor and relay. The processor communicates with the relay for selectively electrically opening and closing the relay upon instructions from the processor. The processor detects a mains electrical power supply and sequences opening of the relay following a pre-set delay upon detection by the processor of an absence of, or loss of the mains electrical supply to the processor and the relay. A removable key cooperates with the processor and relay for the manual closing of the relay to power the power tool.