Learn in the textbookDetection Devices (Light, Electromagnetic, and Motion Sensors)
DefinitionA magnetic sensor (磁気センサー) detects the strength and direction of the magnetic field around it.
ExplanationA magnetic field is the region around a magnet or an electric current where magnetic force acts. The Earth produces a weak field of its own, so measuring its direction with a magnetic sensor reveals which way is north; this is how a smartphone's electronic compass shows your heading in a map app. Fix a magnet to a door, and the same kind of sensor can also tell whether the door is open or shut from whether the field is present.
AnalogyIt is a pocket compass that reports north with an electrical signal instead of a needle.