MC-38 Wired Door Window Sensor Magnetic Switch

The MC-38 Wired Door/Window Magnetic Sensor is one of the most popular and reliable reed switch sensors used in home security and electronics projects. The sensor consists of two parts: a reed switch housed in a small ABS plastic enclosure (with two wires attached) and a separate magnet in an identical-looking enclosure. When the two halves are placed close to each other, the magnetic field activates the reed switch, closing the circuit. When the two halves are separated by more than the activation distance, the switch opens and the circuit is broken.

This simple but effective mechanism makes the MC-38 ideal for detecting the opening and closing of doors, windows, drawers, cabinets, gates, mailboxes, refrigerators, and any other moving panel. It is widely used in commercial alarm systems, home security setups, smart home automation, and DIY electronics projects.

The sensor operates at a maximum distance of 15mm (~0.6"), meaning the magnet can trigger the switch reliably even with a small gap between the two halves — useful when mounting on slightly imperfect surfaces or where some clearance is needed. Both halves include mounting tabs and screw holes, but they can also be installed using double-sided foam tape for non-invasive installations.

The MC-38 is passive — it requires no power to operate. The reed switch simply behaves as a normally open (NO) switch that closes when in proximity to the magnet. This makes it extremely easy to use with Arduino, ESP32, ESP8266, Raspberry Pi, and any digital input pin (using a pull-up or pull-down resistor configuration). It is also fully compatible with traditional wired alarm panels.

The sensor is rated for up to 100 mA at 200 VDC maximum, which is more than sufficient for low-voltage signaling in microcontroller and alarm applications.

Wiring Logic:

• Magnet near sensor → Reed switch closed → Circuit conducts
• Magnet away from sensor → Reed switch open → Circuit broken

Specifications

• Sensor Type: Reed Switch with Magnet (Wired)
• Switch Configuration: Normally Open (closes when magnet is near)
• Activation Distance: Up to 15 mm (0.6")
• Rated Current: 100 mA (Max)
• Rated Voltage: 200 VDC (Max)
• Cable Length: 25 cm (~10 inches)
• Enclosure Material: ABS Plastic
• Color: White (typical)
• Sensor Box Dimensions (each side): 27 x 14 x 8.7 mm (1" x 0.55" x 0.34")
• Weight (per side): ~5.2 g (0.18 oz)
• Mounting: Screw holes (screws may be included) or double-sided tape
• Compatibility: Microcontrollers, alarm systems, smart home controllers

Applications

• Home security alarm systems — wired and wireless
• Door, window, gate, and garage door open/closed detection
• Drawer, cabinet, and locker open detection
• Refrigerator and freezer door monitoring
• Mailbox open notification projects
• Smart home automation (with Arduino, ESP32, Raspberry Pi, Home Assistant)
• IoT-based door/window monitoring
• Burglar alarm and intrusion detection systems
• Office and warehouse security monitoring
• Pet door open/close detection
• Industrial automation — limit switching with magnets
• Educational STEM and electronics projects
• DIY automatic light switches (light turns on when door opens)
• Smart locks and access logging system