Door contact sensor BLOW 4557# (reed switch) HO-03G brown

The BLOW door contact sensor HO-03G (reed switch) in brown is a wired magnetic sensor designed to detect the opening and closing of doors or windows. Its compact, low-profile housing allows discreet installation on door and window frames and sashes. The sensor operates as a normally-closed reed switch that changes state when the magnet is separated, producing a contact closure signal compatible with standard alarm control panels and monitoring devices.

Advantages

The device offers reliable mechanical switching with minimal electronic complexity, ensuring long-term stability and predictable performance. Its small dimensions and neutral brown finish make it suitable for unobtrusive mounting on wooden or painted surfaces. As a wired sensor, it provides a continuous connection to security systems without the need for batteries, reducing maintenance requirements and offering consistent signal transmission.

Suitable for

• Wired alarm systems for residential and small commercial properties
• Perimeter protection of doors and windows
• Access monitoring in offices, storage rooms, or cabinets
• Retrofit installations where discrete, low-profile sensors are required

Key specifications

• Type: Reed switch (magnetic contact)
• Connection: Wired (contact closure output)
• Color: Brown
• Mounting: Surface mount on frame and sash
• Form factor: Compact, low-profile housing for discreet installation
• Operating principle: Changes contact state when magnet is separated

How to use

Install the sensor body on the fixed frame and the magnet on the moving sash so that the two parts align when the door or window is closed. Connect the sensor wires to the corresponding input on the alarm control panel or monitoring device following the panel manufacturer’s wiring diagram for normally-closed contacts. Verify correct operation by opening and closing the door or window and confirming the panel registers the change of state. Secure the components with screws or adhesive according to the mounting surface and ensure wiring is routed to avoid pinch points.

Usage recommendations

Place the sensor where the magnet and reed switch meet without gaps larger than the manufacturer’s suggested alignment — proper alignment ensures reliable detection. Avoid installing the sensor near strong electromagnetic sources or where mechanical strain may damage wires. For exposed exterior doors, use protected routing and suitable sealants to prevent moisture ingress into cable entry points.