Power is applied to lock a door.
When you remove power, the lock unlocks.
Electromagnetic locks are only available Fail Safe.
Should be used on stairwell doors requiring re-entry and must allow free egress with fire alarm activation or power failure.
Power is applied to unlock a door.
When you remove power, the lock locks.
Exit Devices with electric latch retraction are only available Fail Secure.
Should be used on doors where entry security is a concern since the default state is to remain locked.
Regardless of whether they are fail safe or fail secure, most electrified door hardware products - with the exception of maglocks - allow free egress at all times.