Captive Double Cylinder

Best suited for doors that have glass panes on or near the door. It combines the best features of a single and double cylinder deadbolt all in one. The captive double cylinder lock uses a cylinder on the inside and the outside of the door. When an occupant wants to lock the door from the inside, a special captive thumbturn key is inserted into the inside cylinder and the bolt is thrown. At that point the key is held captive in the inside cylinder and cannot be removed. This is to ensure that the "key" is readily available to instantly unlock the door in an emergency. This design is especially well suited for homes with small children. If the building is unoccupied, the captive thumbturn can be removed to prevent an intruder from breaking glass panes, on or near the door, to reach in and unlock the door. To release the captive thumbturn key, the door has to first be unlocked and a second key has to be inserted in the outside cylinder and turned 90 degrees. This action will release the captive thumbturn key and cause the lock to operate as a double cylinder deadbolt. Caution: the double cylinder function should only be used when the building is unoccupied. Always check local building codes.