Adafruit Magnetic contact switch (door sensor)

*PLEASE NOTE THIS PRODUCT HAS BEEN DISCONTINUED* This sensor is essentially a reed switch, encased in an ABS plastic shell. Normally the reed is 'open' (no connection between the two wires). The other half is a magnet. When the magnet is less than 13mm (0.5") away, the reed switch closes. They're often used to detect when a door or drawer is open, which is why they have mounting tabs and screws. You can also pick up some double-sided foam tape from a hardware store to mount these, that works well without needing screws. TECHNICAL DETAILS

• Normally open reed switch
• ABS enclosure
• Rated current: 100 mA max
• Rated voltage: 200 VDC max
• Distance: 15mm max

Dimensions:

• Box size (each side): 29mm x 14mm x 9mm / 1.1" x 0.6" x 0.4"
• Cable Length: 305mm ? 12mm / 12" ? 0.5"
• Weight (per side): 5.4g

Netduino driver and Netduino sample. This sample shows how to use an interrupt handler to respond to a button press or a magnetic contact switch closing.