Keyhole locks

How secure were the so-called "keyhole locks" for old fashioned bit key locks? The few examples I've run across as a lock and key collector looked fairly crudely made, and I find it hard to imagine there were very many different keys produced. I can imagine that if someone had a keyhole lock key, he/she probably had what amounted to not much more than another "skeleton key", meaning that he/she could use it to open a wide variety of keyhole locks out there. Am I right or wrong?

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You are right and wrong. Better, more secure and complex locks were made and sold, but for the most part the ones that survive today are the more simple type that you will find in older homes. Most of these locks used different levels of warding to distinguish one key from the next so one house might have originally had an individual key for each bedroom and bath, but the skeleton key (one with all the meat removed) would bypass all the wards.

The correct name for these are bit key locks and were made in rim (secured to the inside of the door with screws.) and mortise (Fit into a pocket in the door stile.) configurations.

These fell into obscurity when the key in the knob lock was invented in both the tubular and unit lock configurations as it was much easier to install.

The mortise lock is making a comeback in some areas as it is much easier to design one with lever handles now required by the Americans with Disabilities Act and some building codes that require one twist of the knob or lever to retract the deadbolt.

They still make bit key locks in multi tumbler configurations but they are not common in the US as they are in Europe.

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Roger Shoaf

If you're talking about lever tumbler locks as opposed to simple warded locks some of the lever locks are quite secure. The simple warded ones much less so.

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Also depends on type of lever lock. For example a 2 lever door lock may have only 2 differs off the levers, 6 off a bullet ward, and the range can be operated with two skeleton keys. They are almost as easy to pick as a warded lock. A four lever lock with a 5 cut symmetrical key may be little better with 2 or 4 differs off levers and a dozen off sash wards.

A 5 lever 7 cut symmetrical key lock has 1000 differs, this being a minimum requirement by British insurers.

6+ levers operated one side only can range from 144 or so for drawer locks to many thousands for vault and safe deposit use.
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Presumably the number of changes would be limited by physical dimensions, eg 4 pins with 4 depths would give 200-250 usable differs.

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The original question seems ambiguous. This post answers one meaning. Locks with a traditional 'keyhole shape' keyhole made with warded mechanisms were generally of modest security, but with many different sizes, numerous skeleton keys would be needed to cope will any which might be met. Strong springs, and rust, mean picks need to be quite robust.

Modern door locks with a plurality of movable detainers (because not all are traditional lever mechanisms), and incorporating some pick-resisting features, such as widely used in Britain, are likely to be more secure than many door locks used in the USA.

The other possible meaning is the value of 'keyhole blocking locks', made to block the large keyholes of warded locks. Yes, most modern ones are small, with a pin tumbler mechanism, but unless one has a large selection of keys to try, of the correct keyway, they are a considerable obstacle. Their small size makes them awkward to pick.

In the past, the earliest versions used very high quality key mechanisms. The first one was invented by Samson Morden in 1841, using a Bramah lock. Soon afterwards, others were made using E. Cotterill's Climax mechanism.

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