A latching relay is bistable. It can be in the closed state with no coil power applied or it can be in the open state with no coil power applied. It only takes a pulse of 1.5 milliseconds to change from the open state to the closed state; or a 1.5 millisecond pulse will change from the closed state to the open state. A magnet partially biases the reed switch to create the latching states. Generally two coils are used: one is used for closing the contacts and the other is used for opening the contacts.