Abstract: A tire pressure alarm system primarily adapted for the monitoring of tire pressure in the pneumatic tires of coaxial dual wheels on a vehicle including a pneumatic cylinder mounted diametrically on the hub of the outboard wheel and having its end portions coupled by fluid hoses to the air valves of the respective inboard and outboard tires. The cylinder includes a reciprocal piston member normally biased to a axial central position defining air detector chambers at opposite ends of the cylinder for communication with the respective air valve stems. The piston member carries a pair of axially spaced switch elements movable with the piston member for actuating switch sensor elements spaced along the cylinder for generating alarm signals corresponding to predetermined tire pressures in the respective inboard and outboard tires. The pneumatic cylinders are substantially centrifugally balanced on the hub of the outboard wheel.