A double cylinder deadbolt is a deadbolt that you need a key to unlock from the inside instead of having a lever that you turn. DH and I are having a disagreement about putting this type of deadbolt on the doors of our new house. He wants to use a double cylinder, because we have windows right next to the doors, so someone could smash the window and reach in through the broken glass and turn a lever to let themselves in the house. With a double cylinder, they would need a key in order to open the door, so that could keep them from getting in the house. While I can see how that type of lock adds security, I'm worried about it being a fire hazard. Some people don't use them, because if there was a house fire, it could make it more difficult to exit your house. Not everyone can think clearly enough or have the time to use a key to unlock a door during a house fire. We talked about using a regular lever on the front door and the double cylinder on the back doors, which are next to more windows, but I'm still not 100% comfortable with the idea. Do you have a double cylinder lock on any doors in your home?