Replace Your Existing Lock— the M220 Surface-Mount Lock can be used to completely replace an existing deadbolt, latchbolt, or just a plain door knob. Just take off your existing door hardware and install this one in its place. It has been designed to easily retrofit onto standard doors.
Use with Your Existing Lock—you can also leave your existing lock in place and install this lock either above or below it for added security and convenience. If you do this, people who know your secret code will only be able to enter when both locks are unlocked, perhaps, during the day, for example.