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Reed Switch Sensor Module

SKU: FA3028-1
Sensor Type

Hermetically sealed reed switch
Output Type

Digital (HIGH/LOW)
Operating Voltage

3.3V – 5V DC
Contact Type

Normally Open (NO) or Normally Closed (NC) depending on variant
Trigger Method

Magnetic field proximity
Indication

LED indicator
Pin Count

3 pins (VCC, GND, DO)
Module Dimensions

Compact PCB with mounting holes

The Reed Switch Sensor Module is a compact, reliable magnetic proximity sensing board designed for Arduino, ESP32, Raspberry Pi, STM32, and other microcontroller projects. Built around a hermetically sealed reed switch, this module detects the presence of a magnetic field and provides a clean digital output for counting, position sensing, door/window detection, and proximity applications. It is one of the simplest and most durable magnetic sensing solutions available for makers, students, and industrial applications.

At the heart of the module is a reed switch — a small, sealed glass tube containing two ferromagnetic contacts. In the presence of a magnetic field (such as from a permanent magnet), the contacts are pulled together, closing the circuit. When the magnetic field is removed, the contacts spring apart, opening the circuit. This mechanical switching action requires no power to maintain state, making the reed switch an extremely low-power and reliable sensing element with a lifespan of millions of operations.

The module includes signal conditioning circuitry that converts the reed switch’s open/close state into a clean digital output compatible with microcontroller logic levels. The output is typically LOW when a magnet is detected and HIGH when no magnet is present (depending on the module variant), and it can be connected directly to a digital input pin. An LED indicator provides visual feedback when the magnetic field is detected, making it easy to verify operation during setup and troubleshooting.

The module operates from a 3.3V to 5V DC supply, making it compatible with both modern low-power microcontrollers and traditional 5V systems. The compact form factor with mounting holes allows easy integration into door frames, window sashes, equipment enclosures, and custom projects. The screw terminals or pin headers provide secure connections for power and signal wiring.

The Reed Switch Sensor Module is widely used in door and window security systems, position detection, revolution counting, flow meters, speed measurement, proximity sensing, robotic limit switches, and tamper detection. It is also popular in educational projects for teaching magnetic sensing and switch principles.

Important Note: The reed switch is a mechanical device with glass contacts, so it should be handled carefully to avoid breakage. The sensitivity depends on the strength of the magnet and the distance between the magnet and the switch — keep the gap as small as practical for reliable detection. Unlike Hall Effect sensors, reed switches have no polarity and can be triggered by either pole of a magnet. The module is not waterproof and should be kept dry. For high-vibration applications, consider a Hall Effect sensor as an alternative.

Whether you are building a door alarm, a revolution counter, or a proximity detection system, the Reed Switch Sensor Module provides a reliable, low-cost solution for magnetic sensing. It is suitable for individual makers, students, and businesses purchasing in bulk for product development or educational programs.

Features

  • Hermetically sealed reed switch — Reliable magnetic detection with millions of operations

  • Digital output — Clean HIGH/LOW signal for easy MCU integration

  • Zero power consumption — Switch requires no power to maintain state

  • LED indicator — Visual feedback when magnetic field is detected

  • Wide voltage range — 3.3V to 5V DC, compatible with Arduino, ESP32, Raspberry Pi

  • No polarity sensitivity — Triggers with either pole of a magnet

  • Compact form factor — With mounting holes for easy integration

  • Screw terminals or pin headers — Secure connections for power and signal

  • Wide application range — Door/window security, position detection, counting, proximity sensing

  • Cost-effective — Affordable solution for magnetic sensing in volume production

Technical Specifications 

# Parameter Specification
1 Sensor Type Hermetically sealed reed switch
2 Output Type Digital (HIGH/LOW)
3 Operating Voltage 3.3V – 5V DC
4 Contact Type Normally Open (NO) or Normally Closed (NC) depending on variant
5 Trigger Method Magnetic field proximity
6 Indication LED indicator
7 Pin Count 3 pins (VCC, GND, DO)
8 Module Dimensions Compact PCB with mounting holes

Usage

Getting Started

  1. Connect power — Supply 3.3V or 5V DC to the VCC pin and GND to ground.

  2. Connect the output — Connect the DO pin to a digital input on your microcontroller (e.g., D2 on Arduino).

  3. Mount the module — Secure the module to a door frame, window sash, or equipment enclosure. Attach a magnet to the moving part (door, window, etc.).

  4. Upload a test sketch — Read the digital output and observe the state change when the magnet approaches.

  5. Implement control logic — Use the output to trigger alarms, count events, or detect position.

Pin Connections

Module Pin Function
VCC Power (3.3V–5V)
GND Ground
DO Digital output (switches when magnet detected)

Output Logic (Typical)

Condition Output State
Magnet detected LOW (or HIGH, depending on variant)
No magnet HIGH (or LOW, depending on variant)

Example Arduino Code

cpp
#define REED_PIN 2

void setup() {
  Serial.begin(9600);
  pinMode(REED_PIN, INPUT_PULLUP);
}

void loop() {
  int sensorValue = digitalRead(REED_PIN);

  if (sensorValue == LOW) {
    Serial.println("Magnet Detected!");
  } else {
    Serial.println("No Magnet");
  }

  delay(100);
}

Typical Applications

  • Door and window security — Detect opening and closing

  • Position detection — Confirm the position of moving parts

  • Revolution counting — Count rotations of a magnetic target

  • Flow meters — Count pulses from a magnetic impeller

  • Speed measurement — Calculate RPM from pulse frequency

  • Proximity sensing — Detect the presence of magnetic objects

  • Robotic limit switches — Detect end-of-travel positions

  • Tamper detection — Detect unauthorized opening of enclosures

Notes for Business Buyers

  • Zero power consumption — The reed switch requires no power to maintain state, ideal for battery-powered applications.

  • Extremely durable — Hermetically sealed contacts resist corrosion and wear.

  • Simple interface — Single digital output connects directly to any microcontroller.

  • Suitable for bulk purchasing — Ideal for security system manufacturers, flow meter makers, and educational institutions.

Q: What is the Reed Switch Sensor Module used for?

It is a magnetic proximity sensor for detecting the presence of a magnetic field, used in door/window security, position detection, revolution counting, and proximity sensing.

Q: How does a reed switch work?

A reed switch consists of two ferromagnetic contacts in a sealed glass tube. When a magnetic field is present, the contacts are pulled together, closing the circuit. When the field is removed, the contacts spring apart, opening the circuit.

Q: What voltage does the module require?

It operates from 3.3V to 5V DC, making it compatible with Arduino, ESP32, Raspberry Pi, and other microcontrollers.

Q: Does the reed switch require power to operate?

No. The reed switch is a passive mechanical device that requires no power to maintain its state. The module’s signal conditioning circuitry does require power, but the switch itself is passive.

Q: Does the magnet need to be a specific polarity?

No. Unlike Hall Effect sensors, reed switches have no polarity and can be triggered by either pole of a magnet.

Q: What is the recommended gap between the magnet and the switch?

Keep the gap as small as practical for reliable detection. The maximum gap depends on the magnet strength and switch sensitivity — typically 5–20mm for common magnets.

Q: Can I use this module with an Arduino?

Yes. Connect VCC to 5V, GND to GND, and DO to a digital pin (e.g., D2). Use digitalRead() to detect the magnet.

Q: What is the lifespan of the reed switch?

Reed switches are rated for millions of operations when used within their specified electrical and mechanical limits.

Q: Is the module waterproof?

No. The module is not waterproof and should be kept dry. The reed switch itself is hermetically sealed, but the module circuitry is not.

Q: Can I purchase in bulk for a product development project?

Yes. This module is suitable for both individual users and business purchasing, including security system manufacturers, flow meter makers, and educational institutions.

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