Sensor and Relay Magnets

Magnets provide the magnetic field detected by many types of sensors and switches. They can be used to indicate position, proximity, movement, rotation, speed or whether something is open or closed. Common applications include reed switches, Hall effect sensors, magnetic switches, relays, encoders, pickups and proximity sensors.

The effect depends on the type of sensor. A reed switch uses a magnetic field to operate contacts inside the switch, while a Hall effect sensor detects a magnetic field electronically. Learn more about both technologies in our Reed Switches and Hall Effect Sensors article.

Small neodymium magnets are commonly used to activate reed switches because they produce a strong magnetic field from a compact size. The appropriate magnet size and strength depend on the sensitivity of the reed switch, the distance between the magnet and switch, and the orientation of the magnet.

Neodymium magnets are often paired with Hall effect sensors because their strong magnetic fields can be detected from a relatively small magnet. Magnet size, strength, pole orientation and distance from the sensor can all affect the magnetic field measured by the Hall sensor.

The required distance depends on the magnet's size and grade, its pole orientation and the sensitivity of the sensor. Magnetic field strength decreases as the distance from the magnet increases, so sensor applications should be tested using the actual magnet, sensor and operating distance of the finished design.

Magnets and magnetic sensors can be used in motors, alarms, position sensors, rotation detectors, switches and measurement devices. See our Brushless DC Motor, Raspberry Pi Alarm System and Make a Magnetometer projects for examples of magnets used with reed switches and Hall effect sensors.