The REV Robotics Magnetic Limit Switch is a three-sided active-low digital hall effect switch with three internal hall effect elements located on the top and sides of the sensor. The three elements are connected in parallel so that any one of them will trigger the sensor.
Hall effect sensors detect the presence of magnetic fields. The REV Magnetic Limit Switch is an omnipolar momentary switch meaning it will trigger when there is sufficient field strength of either magnetic pole (north or south) detected. 
Specifications
Sensor Type: Digital, Active-low
Voltage Range: 3.3V - 5.0V
Signal Pinout: n & n+1
Magnetic Polarity: Omnipolar (both north & south)
Typical Trigger Distances*
Top: 10mm
Side: 5mm
Typical Hysteresis*: 5mm
Typical Included Magnet Strength: 4300G (0.43T)
 
*Using the included magnet.
Kit Contents
QTY 1 - REV Magnetic Limit Switch
QTY 2 - Magnet with mounting tabs
QTY 1 - JST PH 4-pin Sensor Cable - 30cm