TPMS is a direct tire pressure monitoring systems (TPMS) that is standard equipment on every vehicle sold in the U.S. after September, 2007. The criteria for TPMS standardization is that the vehicle must have only four wheels (no dual-wheeled trucks or motorcycles), and weigh less than 10,000 lbs.
Direct TPMS use a sensor in the wheel/tire to wirelessly relay pressure back to the driver via a display inside the vehicle. Some vehicles have a digital screen that continuously shows all four tire pressures (five if spare has sensor). Others simply flash a "low tire pressure" light on the dash. Additionally, there are two different styles of sensors for a direct system: a valve sensor and a strap/band sensor. Only valve sensors are used on BMW direct system-equipped vehicles. If you bought an aftermarket SmarTire TPMS, its sensors are held on by a strap around the barrel of the wheel.