MC-33A Normally Open Wired Recessed Door Contact Sensor – Hidden Magnetic Alarm for Doors & Windows

Description

The MC-33A is a recessed (hidden) magnetic contact sensor designed for discreet door and window status detection in wired alarm and DIY electronics projects. As a Normally Open (NO) variant of the MC-33 series, its reed switch circuit remains open (non-conductive) when the magnet is near the sensor body—meaning when the door is closed, the circuit is broken. When the door opens and the magnet separates, the circuit closes, allowing current to flow and triggering the connected alarm panel or microcontroller to register an event. This behavior is the opposite of the Normally Closed (NC) MC-33, which is generally preferred for fail-safe security systems. The NO configuration is better suited for simple Arduino logic where an open door should produce an active signal, or for applications where a closed circuit on intrusion is acceptable. The sensor installs flush into a drilled hole, making it nearly invisible once fitted. It requires no external power and functions as a passive switch, connecting directly to a microcontroller GPIO pin or alarm panel zone input.

Critical Note on Availability: Search results for the MC-33A are extremely limited, and no supplier listing specifically for the “MC-33A” model was found. The MC-33 series is widely documented as Normally Closed (NC) by default, with some manufacturers noting that NO versions are available as options . The specifications below are based on the broader MC-33 recessed contact family. Buyers must confirm with their supplier that the specific unit is indeed Normally Open and verify all electrical and mechanical specifications before purchase.

Features

• Recessed Hidden Installation: Flush-mount design conceals the sensor inside the door or window frame, preserving aesthetics and reducing tamper visibility.

• Normally Open (NO) Contact Type: Circuit closes only when the magnet is removed (door opened), producing an active signal on intrusion—suitable for simple trigger logic in microcontroller projects.

• Passive, Power-Free Operation: No battery or external power required; the reed switch actuates solely through the magnet’s proximity.

• Compact Recessed Profile: Designed to fit into a standard drilled hole (approximately 19mm hole size for some MC-33 variants) .

• Metal-Shielded ABS Construction: Fire-resistant housing with metal shielding for stable performance .

• Wired Connection: Pre-attached wire leads or screw terminals connect directly to alarm zone inputs or microcontroller GPIO.

Technical Specifications