Abstract: In a vehicle tire pressure indicator system, a reed switch mounted on the vehicle frame adjacent a wheel is connected to indicator means in the vehicle. An elongage tubular housing of generally cylindrical outer configuration is disposed on the wheel lengthwise parallel to the axis of the wheel. One end of the housing, the outer end, is attached to the tire valve while the other end carries a covered bellows on the end of which is a magnet. The housing is situated to be adjacent the reed switch each time the wheel rotates. Tire pressure is communicated to the chamber surrounding the bellows inside the cover so that when tire pressure is high, the bellows shrinks and draws the magnet away from the reed switch, not influencing it. When tire pressure drops, the bellows extends, moving the magnet toward the switch, triggering the indicator means. The bellows is sealed by having its single bore plugged with a ball member. The bellows contains a stop limiting its collapsing movement.