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.