TireMinder ManualSome info on TireMinder.
I think most pressure monitors work about the same way. The monitor does not read the tire pressure all the time. Each wheel transmitter send information to the monitor at some update time. TireMinder is about 20 min.(?) between sending information. The updates from each wheel are random. If they were updating all the time the batteries would not last long. The monitor keeps track of the updates. If for some reason it does not get an update it will wait for 2 or 3 cycles before it notifies you of a lost signal. This reduces false warnings. It also means that you will not know that you lost signal for that time. Seems like all brands do the same thing.
If there is a sudden change in tire pressure the monitor will send information as soon as that happens. If I remove a transmitter I will get a tire lost pressure warning at that time. It does not wait for the 20 min update time if that happens.