Anti-pick pins are security pins - commonly spool, serrated or mushroom shaped - fitted inside a cylinder so that picking produces false sets instead of an open lock. They make picking slower and less predictable rather than impossible, and they are one of several properties that define high-security hardware.
A standard pin tumbler lock is a row of pins sitting in a row of holes, and picking one is a matter of lifting each pin to the right height in the right order. The lock is not designed to be hard to do that to; it is designed to be cheap to build.
Anti-pick pins change the feel of the job. Instead of a clean click at the shear line, the picker meets a pin that rotates, binds and drops back - and a lock that lies to the person picking it is much harder to pick.
How a standard pin tumbler is picked
Each pin stack sits in a chamber and is held down by a spring. The driver pin above the key pin has to be lifted until its break point reaches the shear line between plug and housing, at which point the plug can turn.
A picker applies light turning force with a tension wrench and lifts pins one at a time until each one sets. On a plain lock the feedback is clear: the pin sets, the plug rotates very slightly, and the next pin is bound. That clarity is what a security pin takes away.
What a security pin changes
Security pins are shaped so that they cannot simply be lifted to the shear line and left there.
The effect is a false set. The plug rotates further than it should, the picker believes a pin has been set, and the pin then has to be released, rotated back and set again. Doing that across several pins at once is where an amateur stops and a professional slows down considerably.
- The pin catches on the chamber wall instead of sliding cleanly.
- The break point sits where the pin cannot reach the shear line directly.
- The plug over-rotates, which feels like progress and is not.
The common profiles
Three shapes account for most security pins in use, and they are frequently combined in one cylinder.
- Spool pins have a narrow waist. The plug turns into the waist and the pin has to be counter-rotated before it will move.
- Serrated pins have multiple small grooves, each of which clicks like a set pin, so the feedback becomes a series of false positives.
- Mushroom and T-pins have a widened head that binds against the chamber in the same way a spool does, with a different feel at the pick.
What anti-pick pins do not do
They do not make a lock unpickable. A skilled picker will still get through a cylinder with security pins; they will simply need more time, more feel and more attempts, and time is the thing an attacker working at a door does not have.
They also do nothing about drilling, forcing or a door that is not fitted properly, and nothing about key control. If the same key opens every door on a site and copies have been handed around, the pin profile inside the cylinder is not the problem.
That is why high-security locks are described by several properties together - pick resistance, drill resistance and restricted keyways - rather than by one of them alone.