A latching relay is an electromechanical switch. Latching relays are electronic parts that are used to control large flow of electrical current with smaller flow of current. Relays are typically used when small continuous electrical currents must be used. A latching relay, however, is used to control large currents with smaller ones, using a pulse to move the switch that then stays in position, and this reduces the power requirement slightly.
Latching relays have a small metal strip that, in essence, revolves between two terminals. Solenoids, or small coils of wire, can be found on either side of a magnetized switch that has one input and two outputs at these terminals. The switch can be used to toggle one circuit on and off, or it can be used to switch power between two circuits. It's the coils that control the relay action.
When an electrical flow goes into the coils, that current generates a magnetic field which turns off. The magnetic strip between the two coils is also exposed to the magnetic field, so that when the circuit causes a pulse of electrical current through these coils, it then pushes the switch mechanism from side to side.
The metal strip remains in that position until it receives another magnetic pulse, but this time in the opposite direction. This action will push the switch back to the other terminal. This type of relay remains in the last position it was in when the current was removed.