Someone wanting to enter the room or building must activate the strike, but it is unlocked for anyone wanting to exit, generally using a panic bar or other device. In case of an emergency, the room or building can be vacated even if the electricity is off.
Using a hinged piece of metal, the lock must have an electric signal to move the metal piece allowing the door to open (unlock).
There is a small motor inside this piece that activates the trigger to let the movement lock. The motor can be operated by a card reader, keypad, fob, or wireless sensor.
This apparatus has a number of benefits.
It provides security for anyone who wants to enter but does not have the authority.
It is less expensive than a magnetic lock.
Importantly, it will provide protection in the event of an electrical outage to allow the people inside to exit but will prevent vandals or looters.