Abstract: A device adapted to be directly connected to the valve stem of automobile tires to indicate a low pressure condition. The device comprises a light, a battery, and a compressionable spring switch assembly uniquely responsive to a low pressure condition in the tires for operating the switch assembly thereby connecting an electrical circuit to energize the bulb. A fail-safe feature immediately prevents the loss of fluid pressure from the tire being measured should the device be damaged either maliciously or by road hazards. The low pressure signals indicated by an energized light are adapted to be seen by the driver through suitably placed mirrors located on the vehicle.