Abstract: An urgent braking device is described which connects in series with a brake light system of a vehicle. The device incorporates power modulating means connected in parallel with an inertial switch. The device is attached to the vehicle with the inertial switch in an orientation relative to the vehicle whereby the switch is normally-closed. The switch opens when the vehicle is decelerating in excess of a predetermined rate. Upon opening, the switch interrupts power supplied to the brake light system and a power modulating means is activated, resulting in a modulated power signal supplied to the brake light system and thereby causing the brake lights to flash.