Door locks and hardware are the locks, handles, hinges, door closers and exit bars fitted to the doors of a building. In the industry, all these metal parts together are called door hardware. In large buildings, more and more doors open with a card or a phone instead of a key.
A door has more parts than most people notice. The lock holds the door shut. A door closer, the arm at the top of the door, pulls the door shut after each person passes. On an emergency exit, a panic bar lets anyone push the door open from inside, without a key or a card. Fire doors, which stop a fire from spreading from one part of a building to another, must close and latch by themselves. In India, the National Building Code sets the rules for exits and fire doors in large buildings.
An electronic lock adds a card reader and a small motor or magnet. When the reader accepts a card, the lock releases. Engineers must decide what each electronic lock does when the power fails. A fail-safe lock opens when it loses power, so that people can escape. It is used on exit routes. A fail-secure lock stays locked when it loses power. It is used on a store room or a server room.
Consider a hotel in Goa with 120 rooms. When a guest checks in, the front desk writes the room number and the check-out time, 11 a.m. on Sunday, onto a plastic key card. The lock on Room 214 runs on batteries and is not connected to any network. It reads the card with RFID, a short-range radio, checks the room number and the time, and opens. At 11:01 a.m. on Sunday, the same card stops working, without anyone touching the lock. The lock also keeps a record of its last few hundred openings, so the hotel can see which card opened the door and when. Many hotels now also send the key to the guest's phone, which opens the lock over Bluetooth. The rest of the software at the front desk is described in hotel technology.
In an office, the locks are usually wired to a network instead. Each lock is connected to physical access control software. That software decides which employee's card opens which door, and changes this at once when someone joins or leaves. The locks also take commands from the building automation system (BAS). When the fire alarm sounds, the BAS releases every lock on the escape routes, so that nobody needs a card to get out.