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From: gwyn@SMOKE.BRL.MIL (Doug Gwyn)
Newsgroups: misc.security
Subject: Re:  Same Key?
Message-ID: <9101072359.AA01068@ucbarpa.Berkeley.EDU>
Date: 12 Dec 90 20:37:49 GMT
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Locks are usually installed near the end of construction.
Often there is a special "construction keying" used that is disabled
after construction is complete; this can involve an extra pin that
comes into effect once the regular key is used, or on large projects
using interchangeable cores, normally the cores are replaced with
the final set after construction is complete.

You should always hire a reputable locksmith to do lock work, not
simply buy locks at a hardware store and install them yourself.
The extra $$ that you pay buys improved workmanship and security.