European Narrow-type and Adjustable Electric Strike lock

1: 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.

2: 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.