Reed switch: A circuit breaker controlled by a magnetic field signal. It has no magnetic disconnect function and the glass tube is fragile. It's used to detect when a flip or slide phone is on or off. If the phone's flip is closed, the software disables any functions covered by the flip, such as the keyboard. It can also be configured to answer calls when the flip is opened and hang up when the flip is closed. If the reed switch fails, these functions will cease.

A reed switch is a passive electronic component widely used in various communications devices. It utilizes magnetic field signals to control a circuit switch, also known as a "reed switch." The reed switch's housing is typically a sealed glass tube containing two spring-loaded iron plates. The tube is also filled with an inert gas called rhodium.

Normally, the two reeds in the glass tube are separated. When a magnetic material approaches the tube, the magnetic field lines magnetize the two reeds, causing them to attract and contact each other, connecting the circuit connected to the two pins. When the external magnetic force disappears, the two reeds separate due to their inherent elasticity, disconnecting the circuit. In actual use, a permanent magnet is usually used to control the connection between the two metal pieces, hence the name "magnetron."