This is a small device called a reed switch. When the device is exposed to a magnetic field, the two ferrous materials inside the switch pull together and the switch closes. When the magnetic field is removed, the reeds separate and the switch...
The Hall Effect Magnetic and Proximity Sensor Module can be used to detect the presence (or absence!) of nearby objects such as magnets. This sensor accepts a GND and +5V supply, and has a single digital output which goes low (GND) when a magnetic...