Modern pin tumbler lock cylinder designs have remained the same for a century or more. At the heart of any pin tumbler cylinder is the formation of a shearline after the correct key is inserted. When intersections of the top and bottom pins are all held simultaneously at the outer diameter of the lock plug, the plug can be rotated to operate the lock.
Approximately 50 years ago inventors developed lock cylinders which required more than one interaction with the pin tumblers. Keys were either required to both lift and twist tumblers or to operate a secondary locking system before an operable shearline was accomplished. At that moment the term 'high security' was born.
An additional feature of high security locks is the restriction on duplication of keys. Patents usually remain in effect for 17-20 years. Even though a high security lock cylinder is designed to be virtually pickproof, unrestricted duplication of keys may allow operating keys to end up in in the wrong hands. As a result, a high security lock system is usually recognized by both pick-resistant lock cylinders and a restricted procedure for duplication of additional high security keys.
High security lock cylinders are usually much more expensive as compared to their standard cylinder counterparts due to several factors such as the addition of secondary parts, tighter tolerances, intricate machining and lower volume.
Secure-T Agency (STA) has just introduced an interesting line of mortise/rim and key-in-knob lock cylinders which provide pick resistance, key control plus lower cost when compared with most other high security lock cylinder systems. The lock cylinder system is called Bi-Active. STA refers to their Bi-Active locks cylinders as "something in between."
STA began with a six pin lock cylinder design. Anti-pick spool-shaped drivers are used in all six spaces to provide the best possible deterrence against lock picking. Easy-slide spring covers are included on all Bi_Active cylinder housings to simplify cylinder servicing. Cut-to-cut spacing and depth increments are identical to SC1 dimensions. This allows locksmiths to use standard pin kits and to originate keys using popular code machines.
As example, a C45 card can be used in an HPC 1200 machine or SC1 depth/space dimensions can be used in a Framon 2 machine to originate Bi-Active keys. Standard hold and vary formulas can be used to generate 4096 possible key combinations for a 6-pin Bi-Active master key system.
A second feature of Bi-Active lock cylinders is the use of dimple sidecuts on the key blank. Two sidepins are included with each Bi-Active cylinder. All STA key blanks presently have the same two dimple cut locations in the first two spaces. Side pins contain rounded tips at each end. If a key without dimples is inserted into the lock, the sidepins are moved into small holes in the housing and the plug will not rotate even if the key cut combination is correct. When a key with the correct dimple locations is inserted, the outer rounded tip of the sidepin moves the sidepins out of the holes in the housing and into the dimple areas on the key which allows the plug to rotate.
Bi-Active lock cylinders are drilled to accept side pins at all five possible locations. Locksmiths can machine a dimple in the field at any of the remaining three locations on the key and insert a side pin at that location. STA Keys without the corresponding dimple will then be prevented from operating that Bi-Active cylinder. Sequential use of dimple sidecut locations can also be used to increase the amount of usable combinations in a master key system.
Each Bi-active lock cylinder is furnished with two nickel silver operating keys plus one brass colored 'lockout' key. One space in the lock cylinder contains a ball bearing which is used as a master pin. In normal operation nickel plated operating keys will have a deep cut in that one position and use the ball bearing as a master pin. The lockout key will contain a higher cut in the space where the ball bearing is located. When the lockout key is inserted, the ball bearing will be held in the top pin chamber.
All Bi-Active lock plugs contain a secondary row of recessed holes. Diameters and depths of the recessed holes are designed to accept the small diameter ball bearing but not the larger diameter master pins or driver pins. As the lockout key is rotated, spring pressure from the top pin will move the ball bearing into the recessed hole. The ball bearing will remain in the recessed hole for the life of the lock cylinder or until the cylinder is disassembled for re-keying. The effect is to change the key combination. A deeper cut on the nickel plated keys will no longer operate the lock and the lockout key becomes the new operating key.
'Lockout key' is misleading since the ball bearing transfer feature can be used for several purposes. Ball bearings can be inserted in several spaces in the lock which could allow key combinations to be changed several times without cylinder disassembly. The lockout feature can also be used for construction keying. Workers will have an operating key during construction. When building construction is completed, the lockout key is inserted and rotated once in each lock cylinder. This action parks the ball bearing (master pin) in one of the recessed holes and worker keys will no longer operate.
Bi-Active key blanks have a unique blade shape and are only sold to locksmiths. Each keybow is prepped to accept a color insert so customers can easily distinguish between multiple keys on a key ring. STA also offers personalized Bi-Active key blanks complete with individualized locksmith business names or logos.
To simplify stocking, STA Bi-Active lock cylinders contain parts for several applications. The two-in-one rim and mortise cylinder is furnished with a standard mortise cylinder cam and collar plus parts for converting the threaded housing to accept furnished rim tailpiece, retaining screws and backplate. Key-in-knob cylinders are furnished with tailpieces for conversion to either a double-cylinder deadbolt, single cylinder deadbolt or knob lock.