Magnetic Reed Switch (Kontakttron) KN-04C — cylindrical sensor, normally closed, compact form

The Magnetic Reed Switch (Kontakttron) KN-04C is a compact cylindrical sensor that responds to the presence of a magnetic field. Configured as a normally closed (NC) reed contact, it is intended for basic proximity detection and security monitoring applications such as door and window sensors or simple position sensing in confined spaces. Its small diameter and cylindrical shape allow for installation in narrow frames, housings, or recesses where larger switches would not fit.

Advantages

The KN-04C reed switch offers a low-profile cylindrical design that simplifies discreet mounting and integration into door and window frames. As a normally closed contact, it provides a defined default circuit state that can be monitored for open/closed conditions. The mechanical reed construction ensures passive operation without the need for onboard power, providing reliable switching when a compatible magnet approaches. Its compact dimensions reduce the need for structural modifications during installation.

Suitable for

• Door and window alarm contacts in residential and light-commercial systems
• Position sensing in small enclosures or housings
• Simple proximity detection in automation or DIY electronics projects
• Replacement of larger reed switches where space is limited

Key specifications

• Switch type: Normally closed (NC) magnetic reed contact
• Form factor: Cylindrical, compact body suitable for recessed mounting
• Operation: Magnet-actuated proximity switching
• Connection: Leads suitable for wiring into alarm circuits or low-voltage systems
• Typical use environment: Indoor installations, protected from direct moisture ingress

How to use

Mount the KN-04C sensor in the fixed part of the installation (frame or housing) so that a separate magnet can be positioned on the moving part (door, window, or panel) to actuate the contact when closed. Wire the sensor leads into the alarm or monitoring circuit according to the system's wiring diagram, taking account of the normally closed behavior so the controller or alarm panel can detect an open circuit. Ensure the magnet aligns with the switch when the moving part is in the closed position and verify correct operation by opening and closing the moving part while observing the system response.

Usage recommendations

For reliable operation, select a magnet with appropriate strength and ensure correct alignment and distance between magnet and switch. Protect the sensor from direct exposure to liquids and excessive mechanical stress. Use in low-voltage alarm and monitoring circuits; avoid connection to high-voltage mains circuits. Test the installed contact periodically as part of routine maintenance to confirm consistent switching behavior.