Abstract: A tire pressure monitoring system for a tractor-trailer type vehicle includes a series of sensors on each of the wheels of the vehicle. When a low pressure condition occurs, the sensor activates a radio frequency transmitter for delivering a low power FM signal to a receiver on the tractor. A delay circuit is incorporated in the receiver to require that the signal from the transmitter last for a predetermined duration prior to energizing an indicator in the tractor. The receiver antenna is preferably mounted on the bottom of the tractor in a plane including the trailer wheels.