A radar activated brake light device to be integrated into a vehicle to alert drivers of potentially hazardous changes in traffic speed consisting of a radar device to measure the speed of a forward vehicle; a sensor input from the speedometer of the host vehicle; a computer processor to evaluate the data for potentially hazardous speed changes; a luminous display mounted on the host vehicle to warn the driver of a trailing vehicle; and, optionally, a warning light and warning buzzer mounted internally to the host vehicle to alert the driver of the host vehicle of potentially hazardous speed changes.