My BMW has them.
Driving down the autoroute on holiday in France, and the light comes on.
All family in car, packed to the rafters.
Stop, look around at each tyre, and I haven't a clue which tyre has supposedly gone flat, only way to tell is too check the pressure in each tyre, and, you guessed it, I have no pressure gauge.
Reset the system, and continue, fingers crossed.
It did not come on, and when we got to relatives and checked the pressures, all okay.
Over the last two years I have had two proper flats, and six false alarms.
On both occasions because I have had proper flats and no spare tyre, both tyres ended up being scrap after driving to the nearest tyre dealership.
Fortunately as a company car, straight onto the company Visa card thank goodness!