Just for everyone else's enlightenment since there is also an ongoing PM between Sarah Lichtman and me, my sensors work immediately if I take one off the valve stem. That sets off the "Low Pressure" alarm. But if I take the tire off and move it out of range of the monitor, it can take an hour before the monitor notifies me that my tire is missing. During that hour while the tire is out of range I can remove the sensor and there will be no notification of "Low Pressure". Not a good thing IMO. Just too long of a time lag.