This paper describes two types of tire pressure warning devices, TWD-I and TWD-II, that are low in cost and are easy to install on a vehicle.
TWD-I has a buzzer and a dry-cell battery that are attached on the inside of the wheel center cap. They are connected to a pressure switch that is attached to the air valve stem after the tire is filled with air to the prescribed pressure. If the pressure drops below a certain level, the switch sends a signal that energizes buzzer. TWD-II is a kind of monitor that indicates a drop in tire pressure by changing the color of the wheel center cap through the action of a diaphragm and a magnet.
In comparison with conventional innovations, the two new warning devices offer the advantages of lower cost and easier installation on vehicle.