Deadbolts are a must have to securely lock any exterior door. Deadbolts are key to keeping your mind at ease if away from your home or office, and are very important for any business for maintaining security. There are 4 main types of deadbolts, each different depending on the application or preference.  width=Single Cylinder are the most common, as they would work on any application and are the most affordable. Single Cylinder deadbolts require a key to unlock and lock the door. And the door can also be unlock and locked with a simple turn of the thumbturn from the inside.    width=Double Cylinder deadbolts have keyed cylinders on both sides of the door, which requires a key to unlock and lock from both sides of the door. These are not recommended for just any door, because if there was an emergency you would need your key handy before being able to unlock the door to escape. This style is mainly used on doors that are part glass. It's a comfort for people to know that if an intruder were to break the glass, they would need a key to unlock the deadbolt. Single Sided deadbolts are often confused with the single cylinder, but they are completely different. Single sided deadbolts have only a thumb turn on the inside of the door and is blank on the outside of the door. These require special prepping for the door, where the bore hole is not drilled all the way through the door, but only half of the door. If your door already has a bore hole completely through the door, then this style will not work on that door.  width=Keyless Electronic/Mechanical Deadbolts are the fancy deadbolts that have the electronic keypad, so all you have to do is remember the code to punch in an unlock the door. These are battery operated, and lots have the light up key pad. Keyless do not require a key to enter, but they have an available keyed cylinder if you wish to use that. You don't have to remember your keys to get inside your home, office or business! Just program a code or several if you need, so easy! Mechanical Deadbolts are pretty much the same thing as the keyless electronic. They have a keypad to punch in a simple code to enter. The only difference is that mechanical do not require batteries or power to operate.