Magnet based Reed switches are used as proximity switches. When a magnet attached to an object brought close to the switch, the magnetic reeds attract to each other and close the switch contacts. A schematic is shown in Figure 2.3.6.

Figure 2.3.7 LED based proximity sensors [1]

Photo emitting devices such as Light emitting diodes (LEDs) and photosensitive devices such as photo diodes and photo transistors are used in combination to work as proximity sensing devices. Figure 2.3.7 shows two typical arrangements of LEDs and photo diodes to detect the objects breaking the beam and reflecting light.