Lock Bumping Protection

January 20, 2008

If you are reading this, then you are probably already aware of the problem.  Lock bumping is an easy way for a burglar to unlock your front door.

There is a way for the do-it-yourselfer to modify a deadbolt to make it bump proof.  This is without any external visible difference.  I modified my deadbolt, and it took a couple of hours, and $11 for a re-keying kit purchased at a local home center.

There is a catch.  You need a deadbolt that has a key where one of the notches is at the highest level.  I’ll explain this later.

 Advantages of this method:

Inexpensive.

Uses a standard key, and possibly your existing key.

It is possible for all your locks to use the same key.

This works on most home deadbolts.

This technique should work on any lock that uses a cylinder, providing the cylinder and internal plug can be removed.

 How it works:

The plug is modified to keep one of the pins above the bump key level.  See Figure 1.  The plug is the small brass piece that the key slides into, rotating to open the lock.  This modification involves inserting a peg into the side of the plug that protrudes into one of the holes.  This keeps the pin from dropping below the peg, and keeps the pin above the level of the bump key.  Since the bump key cannot strike this pin, the cylinder remains locked.

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Figure 1:  Pin above the bump key  

Key criteria:

As mentioned earlier, a key is needed where one of the notches is at the highest level.  See Figure 2.  This allows enough space for the pin to ride above the bump key, and still be raised by the house key.  It is possible that your existing key qualifies.  If not, then when picking out a re-key kit, select one with a key that does.  You can also buy a new deadbolt with a key with a high notch.

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Figure 2:  A key with a high level notch is needed

The following pictures show how to modify the plug to install the peg.

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Pictures 1 and 2:  This shows a Weiser deadbolt.  This procedure works with any brand deadbolt that uses a standard 5 or 6 notch key.  You just need a re-key kit that will work for the brand of deadbolt you are using.  In my case, I used a Kwikset re-key kit for the Weiser deadbolt.

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Picture 3:  Lock removed from the deadbolt

 

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Picture 4:  Plug removed from the lock cylinder

 

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Picture 5:  This is the heart of the task.  Using the pin associated with the highest key notch (shortest pin), mark the location where the side peg will be installed.  This corresponds with the keys high notch point.  This location needs to allow enough depth for the pin to drop below the shear line, and yet above a bump key.  Look at the following pictures, and use your judgment.  In this case, the peg was made from a small nail.  Select a drill bit with the same diameter as the nail.  In my case, the nail was slightly larger than the closest drill bit, so I put the nail into a power drill, and reduced the diameter slightly with a file.  Cut and file the nail (peg) so that it is slightly longer than needed. Before drilling, double check everything.  Put the key into the plug.  Does the high point align with the hole you are going to drill into?  You only get to drill once.  Remove the key and drill the hole into the side of the plug.   

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Picture 6:  Here the hole is drilled, and the peg is ready to install.  Put the key into the plug to keep the peg from going in too far.  Partially insert the peg.  Either press fit, or put a little glue (epoxy) on the peg before final insertion.  Carefully push the peg in until it partially intrudes into the locking hole, but does not touch the key.  I made the mistake of pushing the peg in too far, and had to carefully remove some of the peg with a Dremel.  File off any of the peg that is protruding outside the plug.

  

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Picture 7:  The plug with the side peg installed, and the lock pin laid inside.  Notice that the pin is near the top, but enough below the surface that the locking pin will prevent the plug from turning when a bump key is used.

Make sure the key goes in smoothly, and raises the pin to the correct level.  Insert the remaining pins.  With the key in, all the pins should be level with the top of the plug.  Insert the plug into the lock and try it out.  Reassemble the deadbolt, and again, try it out.  

If you had to use a new key, then you can re-key the rest of the locks using the re-key kit.  The kits usually contain enough pins to do five or six locks.  If it didn’t provide enough pins, you can take the locks to a locksmith to have them matched to your new key.  The cost is usually reasonable.

 Possible questions:

Can I get the re-key kit on line?

If you get the re-key kit through the internet or mail order, then you cannot personally select a key with a high level notch. 

 Do I need a re-key kit? 

If you have a plug follower tube, and know how to disassemble the lock, and do not have to change keys (i.e. existing key has a high level notch), then you do not need a re-key kit.

 What if I screw up this process and need a new plug? 

A local locksmith should be able to provide you with a new plug.  Another option is to buy a new deadbolt.

 What if I really screwed up this process and have pins and mangled springs all over? 

When the re-key instructions says to carefully remove the plug by pushing it out with the plug follower, the instructions are not lying.  Hopefully your local locksmith is sympathetic and will help you out.  Another option is to buy a new deadbolt.

 Can I do my house doorknob (Keyed Entry Knob)?

Your deadbolt should be sufficient.  If you do not have a deadbolt, you should consider installing one.  They are much more secure.  If you want to do a doorknob, the plug is modified the same way as for a deadbolt.  However, some doorknobs are tricky to disassemble.  The re-key instructions explain how to dissemble common doorknobs.

 What if I have one of those real fancy entry locks, such as a number keypad with a key backup?

Use your own judgment.  If you have to re-key it, can you find the kit?  Can you find the instructions and tools needed to remove the plug?  Would this void a warranty? 

 Why don’t these instructions explain how to take the deadbolt apart?

The re-key instructions contain this information, and are specific to a brand of lock.  There are too many different lock designs to cover here.  And of course, there is the internet for information.

 Is the author willing to be contacted?

No.  I spent quite a bit of time on these instructions, so hopefully it suffices.  If this is above your capability, then don’t do it.  There are other alternatives:  An alarm, a big dog, an expensive bump resistant deadbolt.  You are welcome to post comments.

 Where can I get more information?

If you would like more information on lock bumping, YouTube has a number of videos on the problem, and a couple of expensive recommended solutions.  Just visit the following link:

http://www.youtube.com/results?search_query=lock+bumping


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