There are 2 types of Tire Pressure Monitoring Systems employed by cars worldwide:
1. Direct, where there is a wireless transmitter inside the tire as part of the inflation valve, transmitting the tire pressure to a receiver within the car system. The advantage of such a system is that the system is able to read and display the tire pressure. The disadvantage of this system is that the transmitter is prone to failure and overall more expensive. A repair would mean a replacement of the transmitter which would require dismantling the wheel. The pressure indication is not absolute and accurate and is dependent on transmitter condition. The system is this prone to false warning.
2. Indirect, where there is a sensor that monitors the rotational speed of the wheel. This is then compared to the other wheels. If the system senses that one wheel rotates more than the rest by a set margin, it would indicate that the wheel is under inflated and a warning is triggered. Such systems are sometimes referred to as Flat Tire Monitoring System. The rotational sensor is located outside of the wheel. It is more reliable and less expensive that the Direct TMPS. It does not read tire pressure but it does a good job of monitoring under inflation not necessarily a puncture.
Malaysian models has the FTMS.
There are several after-market retrofit kits for the direct system which may not integrate with iDrive.