A wireless warning brake light includes a third brake light with a casing installed therein with plural LEDs and a signal receiver for detecting brake signals emitted by an emitter and for activating the LEDs. The rear side of the casing of the third brake light is provided with adhesive material for gluing the third brake light on a safety helmet. A brake light is disposed with plural LEDs and an emitter. The original brake light of a vehicle is replaced with the aforementioned brake light. When the brake light is started, the emitter will be triggered to emit a brake signal that is detected by the receiver of the third brake light, warning vehicles coming from behind. Thus, the safety of motorcyclists or of the drivers of automobiles is ensured.