Keszoox
Magnetic Reed Switch — 4×28mm, Normally Open (NO), Glass Tube, DIY Electronics (5-Pack)
Magnetic Reed Switch 4×28mm, Normally Open (NO), Glass Tube, DIY Electronics (5-Pack)
Couldn't load pickup availability
Magnetic Reed Switch — 4×28mm, Normally Open (NO), Glass Tube (5-Pack)
These 4×28mm glass-encapsulated normally open (NO) reed switches close their contacts when a magnet is brought within proximity, and open again when the magnet is removed. With no moving parts exposed to the environment, they provide reliable, bounce-free switching for door/window sensors, flow meters, proximity detection, and position sensing applications. The hermetically sealed glass tube protects the contacts from contamination, making them suitable for both indoor and outdoor use.
Key Specifications
| Parameter | Value |
|---|---|
| Dimensions | 4mm diameter × 28mm length |
| Contact Type | Normally Open (NO) — closes on magnet proximity |
| Enclosure | Hermetically sealed glass tube |
| Contact Rating | 10W max (typical) |
| Max Switching Voltage | 100V DC / 100V AC |
| Max Switching Current | 0.5A |
| Operate Distance | ~10–20mm (magnet dependent) |
| Operating Temperature | -40°C to +70°C |
| Quantity | 5 pieces |
Reed Switch Types Comparison
| Type | Default State | On Magnet | Best For |
|---|---|---|---|
| NO (this listing) | Open (circuit off) | Closes (circuit on) | Door open detection, flow meter pulse |
| NC (Normally Closed) | Closed (circuit on) | Opens (circuit off) | Security alarm (tamper detection) |
| SPDT (changeover) | One contact closed | Switches contact | Selector, changeover switching |
Why Choose Reed Switches?
- No external power needed — passive switch, no power consumption when idle
- Hermetically sealed — contacts protected from dust, moisture, and corrosive gases
- Long mechanical life — rated for millions of operations with no contact wear
- Fast switching — operates in <1ms, suitable for flow meter pulse counting
- 5-pack value — sufficient for multiple door/window sensors or flow meter builds
Compatible With / Common Use Cases
- Arduino door/window sensor: Connect reed switch between GPIO and GND with INPUT_PULLUP — LOW = magnet present (door closed), HIGH = door open
- Home Assistant door sensor: Reed switch + ESP8266 (ESPHome) for wireless door/window state reporting
- Water flow meter: Reed switch triggered by rotating magnet on flow meter paddle wheel — count pulses for flow rate
- Bicycle speedometer: Reed switch + magnet on wheel spoke for speed pulse counting
- Limit switch replacement: Contactless position detection for 3D printer or CNC machine end-stop
Frequently Asked Questions
Q: How do I connect a reed switch to Arduino?
A: Connect one lead to a digital pin (e.g., D2), the other lead to GND. In code: pinMode(2, INPUT_PULLUP); When the magnet is near, the switch closes and the pin reads LOW. When the magnet is removed, the internal pull-up holds the pin HIGH. No external resistor needed with INPUT_PULLUP.
Q: What magnet should I use with this reed switch?
A: Use a neodymium (NdFeB) magnet for reliable operation at distances up to 20mm. Ceramic (ferrite) magnets work at shorter distances (~5–10mm). For door sensors, a standard door sensor magnet (included in most alarm kits) works well. The magnet must be oriented with its pole facing the reed switch for maximum operate distance.
Q: Can reed switches be used for AC circuits?
A: Yes — this reed switch is rated for 100V AC / 0.5A. For AC switching, ensure the load is within the contact rating (10W max). For higher AC loads, use the reed switch to trigger a relay or optocoupler rather than switching the load directly.
Package Contents
- 5× Magnetic Reed Switch (4×28mm, normally open, glass tube)
