Door access control: cards, PIN or biometrics?

Every access credential is a trade between convenience, security and the cost of the day it goes wrong. There is no universally correct answer, only an answer that fits the door in front of you.

Cards

Cards are cheap, instantly issuable, instantly revocable, and completely indifferent to whether the person holding them is the person they were issued to. That last property is the whole story. Cards get lent to colleagues, left in jacket pockets, and occasionally cloned.

They remain the correct choice for contractors, for visitors, and for anyone whose access is temporary by design. As a primary staff credential they are weak, because the audit trail records the card, not the person.

PIN codes

A PIN cannot be lost or left at home, which is its single advantage. Everything else about it is a liability. PINs get shared, get observed over a shoulder, and get written on the inside of a cupboard door. When a staff member leaves, the PIN has to be changed for everybody.

We fit PIN as a fallback method, rarely as a primary one.

Fingerprint

Fingerprints cannot be lent, which removes the entire class of failure that undermines cards. They are unaffected by lighting and unaffected by masks. They are affected by gloves, by wet hands, and by roughly one user in twenty whose prints the sensor reads poorly.

The mitigation is straightforward and almost never done: enrol two fingers per user, from different hands, at the point of enrolment. It takes ten extra seconds per person and it removes nearly every subsequent support call.

Facial recognition

Face is contactless, fast, and the only credential that works when a user's hands are full or gloved. At a high-traffic door it is the difference between a queue at the reader and a continuous flow of people.

It is defeated by masks, and it is sensitive to mounting geometry and to backlight in a way the other methods are not. A terminal facing a glass entrance with daylight behind the user will struggle, because the camera meters for the window and the face falls into shadow.

What most real sites end up with

Biometrics for staff, cards for contractors and visitors, and PIN as an administrative fallback. This is why we generally specify terminals that hold all three credential types rather than a device that specialises in one. It costs little more and it means the deployment can adapt when the site does.

The part nobody thinks about

Most access control failures are not authentication failures. They are door failures: a misaligned strike, a door closer that no longer pulls the leaf fully shut, a magnet mounted a few millimetres proud so the seal never completes. A 600lb magnet holding a door that never quite closes is holding nothing at all. Spend as much attention on the door as on the reader.