THE 406 uses an engine immobiliser to help prevent theft. The theft system's transponder is housed in the ignition key head. The engine's primary ECU (electronic control unit) is disabled when the key is removed from the ignition. On start-up the key signal is memorised in the system control module, which sends an unlocking command to the engine control unit. The ignition lock has a hardened front face to resist tampering with tools, while the two-part ignition lock mounting bracket is held by two bolts with self-shearing heads. The door locks are designed to shear and turn rather than actuate if forced. The main key incorporates remote function and opens the boot and glovebox. A secondary, non-remote key is supplied. The Peugeot's VIN identification number is prominently displayed on the top of the dashboard behind the windscreen as an added theft deterrent.