If you're driving a 2008 or newer car, truck or SUV, it has a tire pressure monitoring system (TPMS). The feature became standard on all 2008 and newer models, thanks to the TREAD Act that Congress enacted in 2000 after rollover incidents involving the Ford Explorer and Firestone tires. Some 2006 and 2007 model-year vehicles also have TPMS.
The TPMS symbol is either a cross-section of a tire with an exclamation point in it or an overhead view of a car with all four tires exposed, according to the National Highway Traffic Safety Administration (NHTSA). Because of a variety of considerations from tire companies and automakers, a TPMS warning light isn't required to come on until a tire is 25 percent below the manufacturer's recommended tire pressure. That's also well below the pressure required for safe driving, according to the American Automobile Association.
This situation exists because the recommended pressure for some vehicles is barely adequate to carry the vehicle's maximum load, according to the Rubber Manufacturers' Association (RMA). This means if you're driving on a slightly underinflated tire while carrying a minivan full of high school football players or a pickup truck with a bed full of lumber, that tire could overheat and blow out.