Abstract: A method and apparatus for detecting low air pressure in pneumatic tires on a vehicle and conveying this information to the operator of the vehicle. The invention utilizes a resonating device which creates subsonic, sonic, or ultrasonic air waves when it comes in contact with the rotating sidewall of a tire having undesirably low air pressure. The apparatus provides immediate, dependable warning of potentially dangerous low pressure conditions in tires. Furthermore, the apparatus can be used to detect low air pressure in either of dual mounted tires.