Reed Contact

Use a digital input to monitor a reed switch


The reed contact is a special switch that can be closed (normally open contact) or opened (normally closed contact) by a magnetic field. In combination with a magnet, the proximity of two objects can be detected. For this purpose the magnet is usually attached to a moving object (e.g. garage door) and the reed contact is permanently installed (e.g. garage wall or ceiling). If the magnet then approaches the contact, it closes and the changed state can be detected.

The current state of the reed switch can be easily viewed on the mobile phone with our Sensate Monitor App and a bridge (e.g. an ESP8266 like the ESP-12, NodeMCU etc.). For example, with an Android smartphone, iPhone or even the Apple Watch you can check from anywhere and at any time whether the garage door or a window is still open. This is easily and quickly achieved as a very inexpensive, energy-efficient and individual solution.

Alternative names

Reed switch
Reed sensor

Typical applications

Detection whether window is open or closed (window contact)
Detection whether a door, gate, garage door or garden door is open or closed (door contact)
Detection of mechanical states (part X is close to part Y)
Proximity sensor
Limit switch
Fill level detection

All this is possible with our Sensate Monitor App for Android and iOS without any programming including rules and automatic notifications on the smartphone.

Technical data

The closed design results in a whole range of typical properties (please refer to the respective data sheet for exact data):

  • Very long service life (> 10 billion switching operations)
  • Very low contact resistance ( <100 mΩ)
  • Very high insulation resistance ( >10¹⁴ Ω)
  • High and very low voltages/currents switchable
  • Jeep according to design Robust against water, dust, oil, petrol, …
  • High temperature range (-55°C to +100°C)
  • Available in very small sizes depending on requirements and design

Buy Sensor

  • 30x reed contact (normally open)

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  • 20x reed contact (normally open) with magnet

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  • 5x window contact

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Depending on the desired result, the reed switch can be wired with a pull-up resistor or a pull-down resistor. In this case you should also consider the case of an error (e.g. cable break) carefully. Depending on the application, an opener or a closer should then be used as a reed contact. The following illustrations show normally open contacts. If break contacts are used instead, the logic is reversed.

Connection with pull-up resistor:

Correct connection reed contact with ESP8266 with pull-up resistor

Connection with pull-down resistor:

Correct connection reed contact with ESP8266 with pull-down resistor

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