low-tire-pressure warning 
Low-tire-pressure warning systems alert the driver if the air pressure in a tire becomes too low. In simple systems, a light on the instrument panel will be illuminated to warn of the low-pressure condition. This style uses the wheel-speed sensors from an ABS (antilock braking system) that effectively applies the theory that if a tire has low pressure, it will turn faster than the other tires. That said, in the case of very low-profile tires, the wheel-speed sensor is not terribly effective.

More-advanced systems deploy pressure sensors in each wheel to periodically transmit pressure data to a receiver. If the tire pressure falls below a set level, a warning light is illuminated, and in many cases, the pressure in each tire can be read in a numeric display. The pressure-sensing system is particularly useful for vehicles with run-flat tires that do not go flat when losing pressure.

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