Door contact sensor BLOW 4921# model HO-03C white, magnetic reed switch

Wired door contact sensor BLOW HO-03C in white is a magnetic reed-switch device designed to detect the opening and closing of doors and windows and to integrate with wired alarm and security systems. The sensor consists of a compact two-part housing — a main sensor body and a magnet — that are mounted on a door/window and frame. Its low-profile design and wired connection make it suitable for reliable intrusion detection and access monitoring in residential and commercial installations.

Advantages

The BLOW HO-03C provides a simple and reliable switching mechanism based on a magnetic reed contact, ensuring consistent detection of open/closed states. Its compact two-piece design supports unobtrusive surface mounting and straightforward alignment. The wired interface avoids battery dependence and reduces maintenance needs, while the white finish blends with many door and window frames. The mechanical construction offers stable performance in standard indoor environments.

Suitable for

• Wired alarm and security systems for homes
• Office or commercial access monitoring
• Monitoring of windows, doors, shutters and sliding panels
• Integration into alarm control panels, input zones or relay modules

Key specifications

• Type: Wired magnetic reed switch door/window contact
• Design: Two-part sensor and magnet for surface mounting
• Color: White housing
• Contact operation: Normally closed/normally open wiring options depending on system connection
• Mounting: Surface mount on door/window and frame; compact low-profile housing
• Environment: Intended for indoor use in residential and commercial settings
• Connection: Wired electrical connection for integration with alarm panels

How to use

Mount the sensor body on the stationary frame and the magnet on the moving door or window so that the two parts align within the specified gap when closed. Connect the sensor leads to the corresponding input zone of the alarm or security control panel following the panel wiring diagram and the chosen normally closed or normally open configuration. Verify correct operation by closing and opening the door or window and confirming the control panel registers the state changes. Securely fasten the components with screws or adhesive as appropriate for the installation surface.

Usage recommendations

Install the sensor in a dry, protected indoor location away from direct exposure to weather. Keep the alignment gap minimal and consistent to ensure reliable switching. Use the wired connection to route to the control panel with proper cable management and strain relief. For optimal long-term performance, periodically inspect mounting and wiring connections and ensure the magnet and sensor faces are free from debris or paint that could interfere with operation.