Proximity switches are a type of an electrical circuit that will open or close as it makes contact with or comes into a set range of an object. They are commonly used in manufacturing equipment, robotics and security systems. Four types of proximity switches exist. These include infrared, acoustic, capacitive, and inductive proximity switches. Additional information on these sensors can found
. at: http://sensors-transducers.globalspec.com/LearnMore/Sensors_Transducers_Detectors/Proximity_Presence_Sensing/Proximity_Presence_Sensors_All_Types