Most modern vehicles are fitted with a Tyre Pressure Monitoring System (TPMS). All cars manufactured from 2014 onwards come with TPMS fitted as standard.
TPMS works using a sensor valve in each tyre to monitor the pressures. Any low tyre pressure or a pressure imbalance alerts the driver via a dashboard warning light.
The sensor is triggered if there is a drop in pressure of 6-7PSI, the legal requirement. However, some manufacturers set their sensors to monitor smaller pressure drops to give you an earlier warning.
Like many working parts in cars, TPMS sensors need regular servicing to operate accurately. In most cases, a system fault is the result of battery failure. In short, the more miles driven, the quicker the battery will drain. And, being exposed to the weather, TPMS tyre valves, like standard tyre valves, can become corroded.
More importantly, a faulty TPMS sensor will result in an instant MOT failure. i.e. the warning light displays every time the car is started. The battery should be replaced every four years to prevent this from happening.