An electric strike is an access control device used for doors. It replaces the fixed strike faceplate often used with a latchbar (also known as a keeper). Like a fixed strike, it normally presents a ramped surface to the locking latch allowing the door to close and latch just like a fixed strike would. However, an electric strike's ramped surface can, upon command, pivot out of the way when the lock on the door is in the locked position and the door is opened, allowing a user to open the door without operating the mechanical lock or using a mechanical key. After the door is opened past the keeper, the keeper returns to its standard position and re-locks when power is removed or applied, depending upon the strike's configuration.
Electric strikes are generally available in two configurations:
Fail-secure. Also called fail-locked or non-fail safe. In this configuration, applying electric current to the strike will cause it to unlock. In this configuration, the strike would remain locked in a power failure, but typically the mechanical lock can still be used to open the door from the inside for egress from the secure side. These units can be powered by alternating current, which will cause the unit to buzz, or DC power, which offers silent operation, except for a "click" while the unit is powered.
Fail-safe. Also called fail-open. In this configuration, applying electric current to the strike will cause it to lock. It operates the same as a magnetic lock would. If there is a power failure, the door opens merely by being pushed or pulled. Fail-safe units are always operated with direct current.
Electric strikes are sometimes equipped with buzzers that allow someone outside the door to hear when the door is open. The buzzing noise is typically made by applying alternating current (AC) to the strike instead of direct current (DC). When using a DC powered strike, a buzzer accessory can be added to create the buzzing noise, if desired.
There are many manufacturers of strikes, and there are many things that have to be considered when buying one, i.e., type of jamb, type of locking hardware, whether one requires fail-secure or fail-safe, length of latch, depth of jamb, voltage requirements and the length of the faceplate. In some cases it is better to choose a magnetic lock.
Before using a magnetic lock, the Fire Marshal or appropriate authority should be consulted. There are emergency egress issues that must be addressed before using a magnetic lock. Source