An electric strike replaces the fixed keeper in a door frame with a releaseable one. Powering it lets the latch pass, so the door opens while the lock cylinder and handle stay in place. Strikes suit swing doors with a mechanical lock, and fail-safe or fail-secure behavior is chosen at the strike.
A strike changes one small piece of a door frame and leaves the rest of the hardware alone. That is its advantage, and the reason it has to match the frame it is fitted to.
How a strike releases a door
The latch bolt normally rests in the strike’s keeper. Energizing the strike moves the keeper, the latch is free, and the door opens. Because the lock stays in the door, a key or thumbturn can still operate it from the inside, which is why strikes are common on interior doors.
Fail-safe, fail-secure and the frame
A fail-safe strike releases when power is lost, and a fail-secure strike stays latched. The choice is a life safety decision. The strike also has to suit the frame cut, the latch type and the door’s closing force, or the door will stick or fail to secure.