Abstract: For use with trucks, aircraft and other motor vehicles, circuit apparatus signals, from within a pneumatic tire to a display near the operator, an abnormal tire pressure or temperature. A monitoring transmitter within the tire utilizes a negative coefficient thermistor maintained in thermal contact with the tire to sense an abnormal high temperature, and a bellows-type pressure sensor, internally pressurized to approximately the normal tire pressure, to sense abnormal high or low pressures. If one of these abnormal conditions is sensed, power is supplied from a long-lifetime battery to an FM transmitter modulated by a different selected frequency for each tire, selected by a potentiometer marked for each frequency. These circuit elements are on a circuit board secured to the inside of the tire by an overlaying elastic adhesive material which absorbs shock and thermally insulates the thermistor from the air within the tire.