An electric door 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.