He built this set of no-contact limit switches using a hall effect sensor. The small black package sticking out past the end of the protoboard is the sensor. It is used to detect a magnetic field.

So [Andrew Fentem]’s magnetic hockey project certainly pushes ... Each one contains a Hall effect sensor which triggers the 555 which we’d expect is wired as a monostable, this in turn fires ...

The market for hall-effect current sensors market is anticipated to reach USD 1128.0 million in 2022 and increase to USD 2765.0 million between 2022 and 2032 at a CAGR of 9.4%. Consumer electronics, ...

Each magnetic switch has a magnet inside it, which, when the key is pressed, triggers a change in the Hall effect sensor present either in the lower part of the switch or on the PCB. This action ...