Many homes have entryway doors with a feature that is intended to keep occupants safe from intruders, but actually presents a hazard that can have deadly consequences. A frighteningly high number of home owners don’t even know that the hazard exists. About 30% of the homes that I inspect have this hazard, is yours one of them?

I am talking about double cylinder deadbolt locks (also known as “double keyed”). Double cylinder locks are deadbolts that require a key to lock and unlock them both on the outside and the inside of the home. These are often installed as a security measure, so that an intruder cannot break out a window on the entry door, and then simply reach through and unlock the deadbolt with their hand. In theory, this seems like a good safety. However, there are two major flaws in the design, and one of them can be deadly!

First off, let me address the security aspect of the double cylinder lock-set. Most entryway doors open to the inside of the home. This is standard so that a door cannot be barricaded easily on the outside of the home by an obstruction. The idea is that whether it is a snowbank or another object placed in front of the door, the door can still be pulled open to the inside by the occupant. The downside of this is that the deadbolt lock has a much narrower structure to mount the receiver for the cylinder. As a result, the door may be kicked in relatively easily as the door frame will “blow out” when kicked hard enough (as can be seen on most reality police shows on TV). So even if you have a door with the double cylinder lock-set it is usually only offering a false sense of security at best.

Secondly, and a much more important flaw in the double cylinder lock-set, is that the lock on the interior can be locked and then the key can be removed. This presents a very dangerous situation. Let’s say that a fire breaks out in the middle of the night. You wake to smoke filling your bedroom and alarms going off. You rush to get your family and run down the stairs to escape through the front door. You go to try and unlock the dead bolt but the key is missing. Now with the fire blocking the back exit you are stuck. Fire is often capable of engulfing a house in a matter of minutes, and you may run out of time to even make it to a window and kicking the door out from the inside is nearly impossible. For this reason, you should never have entry door locks that are double cylinder locks. A hand turn knob should always be used on the interior of an entry door.

If your home has employed a double cylinder lock-set on any exterior door, I urge you to replace them immediately for the safety of you and your family.