TPMS stands for Tire Pressure Monitoring System. It is an electronic system that keeps an eye on your tire pressure and warns you when a tire is under-inflated.
This system is a vast improvement over just giving your tires the eye-ball test since it can monitor even small changes in pressure. Low tire pressure affects the handling of your vehicle, can negatively impact stopping distances, can reduce gas mileage, and can cause excess wear that reduces the life of your tires.
In addition, the National Highway Traffic Safety Administration tracks accidents. It blames as many as a quarter of a million vehicles accidents every year from low tire pressure.