A vehicle to vehicle warning system comprises a transmitter associated with a primary vehicle alerting one or more secondary vehicles of its proximity through a receiver. The transmitter may emit a radio frequency signal which activates radio frequency receivers in surrounding vehicles. When in appropriate proximity, the signal is configured to initiate a warning at the secondary vehicle, such as light from a light-emitting device or sound from a sound-generating device. In another form, the primary vehicle includes a passive transmitter and the secondary vehicle includes a multi-frequency resonance tag/circuit having distinct frequencies for detection and discrimination. The passive transmitter creates electromagnetic waves which are generated as it passes by the secondary vehicle housing the multi-frequency resonance tag, setting off the secondary vehicle alarm system.