Tire Pressure Monitoring System (TPMS)
Sensors reporting tire pressure to the driver. Underinflation costs fuel and tire life and is one of the most common defects found on inspection.
A tire pressure monitoring system warns when pressure falls below a threshold. It is standard on light vehicles and increasingly present on heavier ones.
The fleet value is that underinflation is both very common and quietly expensive, costing fuel, shortening tire life and appearing regularly as an inspection defect. Sensors themselves become a maintenance item, needing replacement on a service life of their own and reprogramming when wheels are swapped, which is a detail that surprises shops the first time.