Monit Inductive Wheel Probe
The Monit inductive wheel probe works by detecting the presence of metal as it is brought near the end of the sensor. It is typically fitted to a vehicle's wheel hub so that it senses the back of the wheel studs or other metal detection targets as they rotate past. In this way, it can be used to measure speed and distance on a wide variety of modern, classic and historic vehicles.
Please Note: The Monit wheel probe is fitted with a mini molex plug to interface with the Monit G series computers, if you use in any other application you need to supply 12v+ to the brown wire (...never cut the red wire ;-)