Dual cylinder deadbolts require a key to open the deadbolt from both the inside and outside. The locks have no handle. These locks can create an issue for quick exit if a fire or other hazardous situation occurs.
However, the major drawback of a double-cylinder deadbolt is that it can be a safety hazard in the event of an emergency—such as a fire. Because a key is required on both the inside and the outside, occupants may not be able to quickly and easily escape if the key is not readily available.
Use a single-cylinder deadbolt lock on doors with no windows. Use a single-cylinder deadbolt lock on doors that have a window made of tough modern glass. Use a double-cylinder lock on doors that have a window made of old, weaker glass.
The main advantage of installing double-cylinder locks is enhanced security. That's because doors with adjacent windows or glass panels can be broken, allowing intruders to reach inside and unlock the door manually. This is a significant weakness in terms of commercial break-ins and residential burglaries.
A double cylinder deadbolt lock or a single cylinder deadbolt lock without a turnpiece may be used in “Group B” occupancies as defined by the California Building Code.
Security — Since a key is required to unlock them from both the inside and outside, double-cylinder deadbolts offer an extra layer of security. Deters burglars — Since they are more difficult to pick, most burglars will move on to an easier target.
A single-cylinder deadbolt is the most common type. It requires a key to operate the lock from the outside, but has a thumb-turn on the inside.
In the U.S., there is no single comprehensive law against dual-cylinder deadbolts. Individual cities and states have local property and fire codes that may prohibit the use of dual-cylinder deadbolts. The code may prohibit the use of dual-cylinder deadbolts in some buildings and allow them in others.
Double-cylinder deadbolts are acceptable in some locations.
Using a deadbolt that requires a key to unlock it from the inside seems like it would negatively impact egress, but in certain applications it is allowed by code.
If an intruder is in the home, a double-keyed lock can trap the home's occupants in the home with the intruder. Fire codes in some homes prohibit the use of double-keyed deadbolts on egress doors. In rental houses, it's crucial to take into account the liability of using double-keyed deadbolts.
CR's take: The Medeco Maxum 11TR503-19 is the strongest deadbolt across all of our lock categories. It's top-notch for drilling, withstands kick-ins very well, and is designed in a way that makes it quite difficult to pick.
Single cylinder
This is the most common type of deadbolt used. Single cylinder deadbolts have an exterior keyhole that throws or retracts the deadbolt using a key on the outside. On the inside, you can lock and unlock the deadbolt with the thumbturn.
Single cylinder deadbolts are quite common in residential homes. Such locks use a key slot on one side with a thumb-turn mechanism on the other side; the key slot generally faces the outside of a door. This system also allows you to unlock and lock single cylinder deadbolts using a thumb turn from the inside.
One of the manners in which a deadbolt may be vulnerable to potential burglars is when they are made from certain types of materials. Locks that are composed of a soft metal can be sawed through without a tremendous amount of effort on the part of the burglar.
Kicking the Door Down
You should never kick the lock itself--instead, kick the door itself just above or below the lock. Kicking the lock could break your foot. You can also aim just above the deadbolt or knob if you can't locate a regular lock.
The biggest disadvantage of the cylindrical lock is that it is not typically as strong as the other types of locks. If you don't buy the same brand of lock for your cylindrical lock as well as your deadbolt, you will need two different keys to open your door.
Unfortunately, it has never been easier to break into a property with a standard euro cylinder lock. By simply purchasing basic hand tools from any DIY store a euro lock cylinder can be snapped in just 5-10 seconds.
Note that “double cylinder” locks (with keys removable from the inside) are dangerous and unlawful. Nearly every year in NYC tenants die in fires because they cannot locate the inside key for a double cylinder lock in a smoke-filled apartment. Such locks are an extreme hazard and should never be installed.
Most police departments do not recommend double deadbolt locks for residential use. You may be adding additional security at the expense of personal safety with a double cylinder dead bolt. For example, you could lock yourself in and not be able to escape in case of fire or other emergency.
Though the double-cylinder deadbolt is technically more secure, single-cylinder deadbolts are the better option for most homeowners. This is because when the double-cylinder deadbolt is locked, a key would be required to exit, which becomes a safety hazard in the event of a fire.
Due to the nature of the mechanism, a deadbolt will always be more secure than a doorknob. If you're reading this from home I encourage you to do a simple test: If you have a door with both a deadbolt and a doorknob, open it and then lock both locks while the door is open.
Yes, deadbolts are safe. But you probably actually wanted to know if they were secure. They're about as secure as a cheap lock can be; they are mostly intended as a deterrent to someone casually wandering into your house, rather than to actually keep someone out, if they were determined to get in.
Schlage and Kwikset are two of the most popular lock manufacturers on the market. Both brands make excellent locks that homeowners can easily install, but Schlage locks tend to offer higher security and reliability and are trusted by big businesses.
A privacy door knob is one of the most common types of doorknobs that have locking functionality on each side. These types of doorknobs have a thumb turn lock or a push-button on the interior knob and a small hole on the other side that can be locked or unlocked with a special key pin.