12mm Reed Switch/Sensor

Overview

A 12mm Reed Switch Sensor is a magnetic switch that detects the presence of a magnet and changes its state (ON/OFF).

It is one of the simplest and most reliable contactless sensors used in electronics.

Working Principle

• Inside the sensor two thin metal reeds sealed in a glass tube

• Normally contacts are open (NO)

• When a magnet comes near reeds attract and touch circuit closes

• When magnet is removed reeds separate again

Works purely on magnetic field (no power needed for basic switch)

Infographic Summary

Detects: Magnetic field Voltage: Up to 24V Output: Digital (ON/OFF) Size: 12mm (glass tube) Type: Magnetic switch Response: Instant

Basic Connection

Reed Switch Pin 1 VCC / Signal Pin 2 GND

Acts like a simple switch, so you can use it directly or with a pull-up resistor.

Key Specifications

• Max Voltage: ~24V DC

• Max Current: ~1.2A

• Size: 12mm length (compact)

• Temperature Range: -50C to 140C

• Life Cycle: ~100,000 operations

• Output: Digital only (ON/OFF)

Key Features

• Magnetic field detection

• No power needed for basic operation

• Very easy to use

• Extremely low cost

• Small and lightweight

• Fully sealed (dust & moisture resistant)

Applications

• Door/window security sensors

• Burglar alarm systems

• Position detection (open/close)

• Speed sensors (wheel rotation with magnet)

• Robotics & automation

• Smart home projects

Interfacing with Microcontrollers

Works with:

• Arduino

• ESP32 / ESP8266

• Raspberry Pi

Use digital input pin to detect state change.

Important Notes

• Fragile (glass body handle carefully)

• Requires a magnet to operate

• Limited switching current (use relay for high loads)

• Sensitive to strong magnetic interference

Real-world insight:

Reed switches are simple but can wear out if switching high current frequently (arcing effect).

Reed Switch vs Hall Effect Sensor

for door sensors

Add pull-up resistor (10k) for stable readings

For high durability consider Hall sensor instead