Description:
The magnetic contact switch (3560) is nice and small and is designed for flush or countersink installations.

The switch handles gaps of up to 19 mm inch between the magnet and the switch. The switch will turn the digital input "on" when the magnet is within 19 mm of the switch, and will turn it "off" when the contact is broken by moving the magnet more than 25 mm away. Product has a 45cm white 22AWG cable and comes with a rare earth magnet.

Specifications:
Sensor Type: Proximity (Magnetic)
Detecting Distance Max: 19 mm
Detection Hysteresis Max: 21 %
Sensor Output Switch Type: Normally Open
Cable Properties: 450 mm and 22 AWG
Switching Current Max: 500 mA
Switching Voltage Max (AC): 100 V AC
Switching Voltage Max (DC): 100 V DC

Resources:
More information to be found in the Data Sheet