A deadbolt lock backs up a lockset on entry doors to provide maximum security. Better units have a stainless steel bolt with a roller insert to resist sawing and cutting. The standard length for a bolt to extend into a door is 1-inch. The bolt locks the door into the frame, therefore the longer the bolt the harder it would be for the door to be pried open.
Cylinder locks have a pin tumbler locking mechanism in a cylinder. They are most often used in new installations and as replacements because they are mortised into the frame of the door. Because of the wide range of use they can be installed on heavy entrance doors, apartment buildings and homes with a recommended pin number for the type of door.
A single-cylinder deadbolt is key-operated from the outside and manually operated with a button from the inside. This lock is good to use for solid metal or wood doors.
Double-cylinder deadbolts insure safety with same key-operation from both the outside and inside. Doors with glass panes require a double-cylinder deadbolt to prevent someone from breaking the glass, reaching in and unlocking the door. While you are at home it is suggested that you leave the key in the lock in case of a fire or other emergency. Make sure that you purchase a lock that is designed to fit specific size holes and backset for your door. Backsets refer to the distance between the edge of the door and the center of the handle.