Abstract: A tire pressure indicator for visual observation of tire pressure including a screw-on cartridge containing a spring-biased piston with a movable shield which covers a central indicator pilot when tire pressure is up to requirements. When pressure is below what it should be, the piston retracts to allow the shield to expose the indicator pilot to the view of an observer, thus serving as a warning that inflation is required. The cartridge is composed of three elements: a screw on base, intermediate element and a transparent sealed top cap. A cup-shaped vessel is movable in the intermediate and top cap sections in response to a subjacent diaphragm and pressure in the tire.