Abstract: A vehicle warning device comprises a visual indicator activated by a deceleration sensor upon emergency deceleration of the vehicle. The visual indicator is powered by a base inserted into a vehicle lamp socket. In the preferred embodiment, the base is part of an adapter comprising an adapter socket for receiving the vehicle lamp. The adapter allows installation of the warning device by simply plugging the adapter into the vehicle lamp socket without wiring or mounting changes to the vehicle. The preferred embodiment comprises a stroboscope for providing a highly visible indication of an emergency braking state.