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BS 3621 – Thief Resistant Locks (Key Egress)
This British Standard specifies performance requirements and test methods for a thief-resistant, mechanically operated single-point lock assembly (including locking plates, fixing screws, fitting instructions, cylinders, and protective furniture where appropriate) that: a) incorporates a lock conforming to BS EN 12209 that can be unlocked from the inside without a key thereby only allowing keyless egress, and b) is used in doors, windows doors and entrance doors in buildings.
Lock Functions and Applications:
Since its inception, BS 3621 has always required security from both sides, meaning that, once locked, a key is always required to open the door, whether from the inside or the outside. Recognising that there are situations in which a keyless egress lock (secure only from the outside) can offer acceptable security, as well as safety benefits.
| Standard | Function | Comments |
| BS 3621 | Locked by key from both sides | Provided that the key is removed, this type of lock is secure against operation by intruders reaching through a letter-plate, breaking nearby glazing etc. Best used where emergency escape is not required or where other means of escape exist. |
Source: Door and Hardware Federation (DHF) Best Practise Guide: BS 3621:2007 Thief resistant locks assemblies – Key egress