by Klaiviel » 25 Oct 2010 12:44
Okay so here is an example scenario: I live in an apartment complex and have to give an emergency key to my landlord, but I want to know if and when they use it.
To accomplish this mechanically you need a couple of things: one is a #3 master wafer at .045" thickness, 4 Protecto-key Kwikset Balls which have a diameter of .046", and lastly a residential Schlage lock with which to work.
Now if you are like me you have probably wondered at some point what the function of those milled holes next to the pin stack holes in a typical plug are. It turns out they are used in construction keying so that when a new subdivision is being built carpenters and other builders can get access to all of houses but when the home owner uses their key for the first time it locks the construction key out of the system for good.
This is accomplished in Kwikset systems by using the aforementioned Protecto-key balls which when pushed up into the bible ride along the plug until they fall into this pocket, locking out the construction key.
Lucky for me Kwikset systems advance in bitting by .023" per code and Schlage systems advance in bitting by .015" by code so the same balls that are equivalent to a master #2 pin in Kwikset can be used in Schlage as a #3 master pin (granted they are off by .001" but that should not realistically affect performance).
So in this setup I have taken the KIK cylinder and removed the top retaining tab on top of the bible and for pinning convenience. I have tapped the top of the pin stacks with an 8-32 tap and then capped each individual pin stack with a socket head set screw. I have the lock coded as such: 7-5-X-5-7.
All pin stacks except for number 3 have been coded as normal, in number 3 I have the parts arranged as such: first the key pin a #3; then a #3 master wafer at .045"; then 4 Protecto-key balls each .046" in diameter; then a regular driver pin; spring; and lastly the socket head set screw.
Now this system has three keys. I am interested in first is the user key or my key which has a bitting of 7-5-3-5-7. This key will always operate the lock and will never spring the trap.
The second key is the test key which has a bitting of 7-5-9-5-7 this key will only operate the lock if the trap has not been sprung.
The final key is the emergency key with a bitting of 7-5-6-5-7 this key will always operate the lock it will never deny entry; however when used it will spring the trap by pushing the balls up into the bible and letting them drop into the pocket in the plug which will lock out the 7-5-9-5-7 test key.
So in use maintenance staff on the property will not be able to tell from the key that it will do this ,as the key looks and functions perfectly normal . If I want to see if the emergency key has been used all I have to do is try my test key and if it fails to open the lock then yes the emergency key has been used.
Reseting the system is fairly easy; thankfully I figured out a way to do it without handling the Protecto-balls as they are pain to work with.
Basically, first you uncap pin stack #3 and remove the socket head set screw, the spring, and the driver pin; then insert the emergency key into the lock, turn until you can see the pocket containing the balls through the now empty pin stack; replace the socket head set screw and turn the lock upside down; now turn the key back to the resting position and remove the key; remove the socket head set screw and reinsert driver pin, spring, and lastly replace the socket head set screw again.
Congratulations the system has now been reset. Let me know what you think of this idea. I just finished my prototype last night and so far it seems to function flawlessly.
On the pus side you would not have to fool with cutting a pocket on the plug for the balls to fall into.