EM Lock is short for Electro Magnetic Lock. EM locks works with its physical metal plate and these iron (bracket) plate also comes in different types dependence on the site situation.
There are U shape, L or ZL brackets. Watch out for single or double leaf type doors. Are these doors glass type or sliding type?
Back to EM Locks, well.... EM Lock comes in different strength and the most commonly used or best used is the 600lbs type.
Figuratively speaking, such equipment would require the strength of elephant to break open the door that is fastened by 600lb EM Lock.
EM Lock with its core magnetized part (fastened on the door) when activated would attract the iron plate (fastened on the frame on the wall).
Ensure that the strength stated in the product brochures or as offered by your card access vendors work according to the specifications.
This way, end users are not short changed for what they are paying.
Needless to say, trusted brand that comes with quality is of utmost importance and critical to fulfill one of the security objectives a card access system.