I'd suggest to owners that they do the following test to determine how
well there units react Mick.
The test is to change your tyre pressure and see how long it takes the unit to pick up the change.
This is not as easy as it seems.
I have seen someone showing me how
well theres works, it was a tyre dog system (screw onto valve).
He switched the receiver on then proceeded to quickly screw each sender onto the valve stem - by the time he finished all sensors had readings up onto the display and the unit was declared a sucess.
Fatal error - why because the hand screwing the sensor on acts like an aerial and causes a much enhanced signal.
The only way to do it is to change your tyre pressure to any new value then turn off the receiver and drive the car along an open vacant road.
When there is no traffic around , turn the receiver on and see how long it takes to read the new tyre pressures.
With some units you can wait a long time , then a car passes you, or you cross a bridge with steel railing and you get a sudden reading as the metal refects the signal from the sensor to the receiver.