What is Motorized Latch Retraction or MLR ?

Motorized Latch Retraction is a style of door-latching hardware device utilizing a push bar, or crash bar, as the exit means. This style of lock uses a motor and mechanics to retract the locking mechanism. Used in access control systems and(or) with Auto Door Openers for ADA, MLR-style exit devices are quieter and draw less current than ELR options. This lower current requirement allows for smaller power supplies and standard 18 AWG wire over longer wire lengths. 

The image above is Rim Exit Device. The black steel latch engages with a strike on the door jam, or if a double door, a post is installed between the doors. When a user wishes to leave they push on the bar to retract the steel latch. If scheduled to be unlocked, the access control system retracts the push bar and holds the door unlocked. If a user presents access control credentials to a card reader, then the system retracts the exit bar and the door unlocks.