ACCESS CONTROLHow a keypad and an electric strike open a door

The parts

A power supply feeds the lock and usually the controller. Many systems add a door position switch and a request-to-exit button or sensor. Every door, with or without those, has to have a way to get out from the inside.

• The credential: a code, a card, a fob or a phone.
• The reader or keypad, which reads the credential.
• The controller, which decides whether that credential is allowed through this door right now. On a simple standalone keypad the reader and the controller sit in the same box.
• The lock hardware, which does the physical work: an electric strike, a magnetic lock, or an electrified lock or push bar on the door itself.

What happens when you present a credential

The reader sends what it read to the controller. The controller checks it against its list. If it's allowed, the controller changes the power to the lock for a few seconds. The door can be opened, and then the lock goes back to locked. The door still has to close all the way to be secure.

Electric strike or mag lock

An electric strike replaces the strike plate in the door frame. The door stays latched, and the strike releases the latch on command so the door can be pushed or pulled open. A magnetic lock is an electromagnet on the frame that grabs a steel plate mounted on the door and holds the door shut. It holds while it has power and lets go when power is cut.

Fail-safe and fail-secure: what happens when the power drops

Fail-safe hardware unlocks when it loses power. Fail-secure hardware stays locked. A magnetic lock is fail-safe by nature, and many electric strikes can be set up either way. Both terms describe the outside of the door, the side that needs a credential. On a door with a strike or an electrified lock, the inside handle or push bar normally still lets people out either way. A mag lock has no latch for a handle to pull back, so getting out depends on the parts that cut its power. Which setup a door needs, and whether a mag lock is allowed on it at all, comes down to the building, the fire and life safety codes and the local code authority. Ask them. Don't guess.

Why a door won't release

• On a fail-secure strike, no power or low voltage at the strike when it's told to release. On a mag lock or a fail-safe strike it's the other way around: the power isn't being cut. A multimeter at the lock is the first tool, because it shows what the lock is really getting.
• A wiring fault or a loose connection, often at a splice. When the lock is in the door itself, the spot where the wire crosses from the frame to the door is a common one.
• A strike that isn't lined up with the latch, so the latch is pinched against it and can't release.
• Dead batteries, on a keypad lock that runs on them.
• A controller that doesn't have that credential on its list.

One more thing: even where locksmithing doesn't need a license, access control and alarm wiring sometimes does. Here's what the laws say in Colorado and nearby states.