I've been using the PressurePro tire monitor system for almost 10 years and it has saved several tires that were suddenly losing air. It alarms, shows you which wheel, and displays the pressure so you can decide how soon to stop. The sensors screw onto the valve stems, so installation is quick and easy. Programming and readout is from a small unit that is powered by 12 v. The only negative is that the sensors use a sealed battery that will die in about 5 or 6 years (maybe improved in more recent models), and replacement of the sensor is the only option and a significant expense.