Master Lock DSNRN0615BOX Nightwatch Deadbolt With Bump Stop Cylinder, Satin Nickel Finish Locks out unauthorized keys, cleaning services, repairman, lost or stolen keys Single cylinder deadbolt installs like a standard deadbolt with just a phillips screwdriver When the Nightwatch feature is engaged, the lock cannot be opened from the outside, even with a duplicate key This lock can only be engaged or disengaged from inside the house Features Master Lock's exclusive Bump Stop advanced cylinder technology, virtually bump proof and pick proof