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What is a Knob Lock?

Malcolm Tatum
Updated May 16, 2024
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The term knob lock is often used to refer to either doorknobs that are equipped with an internal lock, or a device that fits over an existing doorknob and makes it impossible to turn the knob in any direction. In both cases, a knob lock helps to make homes, offices, and a wide range of commercial buildings protected from unauthorized entry. Knob locks can also help to prevent young children from harm, when installed properly.

In terms of the different types of locking knobs for doors, two types are commonly employed for entrances and exits to buildings of all types. One type is the key doorknob lock. This is a simple doorknob that includes an internal lock that is operated by inserting a key into the lock component. Turning the key makes it possible to lock and unlock the door, effectively limited access to the building to those who have keys that fit the lock. This is the oldest and most common form of knob lock in the world today.

Knob locks for internal use often utilize a design that is known as a twist lock. Rather than allowing for the insertion of a key, doorknob locks of this type rely on a smaller knob that is situated in the middle of the doorknob. The small knob is turned left or right to lock or unlock the door. Knobs of this type are often used for master bedrooms or bathrooms in private residences.

An electronic version of the knob lock is also gaining widespread usage. This type makes use of a card key that is inserted into a scanner. If the scanner recognizes the card key, it will trip the lock on the doorknob, making it possible to enter the space. Hotels and motels often make use of this approach to guest security, since it is a simple task to re-code the scanner after each guest checks out.

A knob lock can also be a simple device that fits easily over a doorknob. Usually constructed of metal, there are also security locks of this type made with high quality plastics and resins. Parents of young children sometimes find these types of knob locks to be helpful in preventing curious children from entering rooms where they are not allowed, while still allowing adults to move freely around the home. Landlords also make use of this type of knob lock when a tenant fails to pay the rent and is asked to leave the premises.

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Malcolm Tatum
By Malcolm Tatum
Malcolm Tatum, a former teleconferencing industry professional, followed his passion for trivia, research, and writing to become a full-time freelance writer. He has contributed articles to a variety of print and online publications, including HomeQuestionsAnswered, and his work has also been featured in poetry collections, devotional anthologies, and newspapers. When not writing, Malcolm enjoys collecting vinyl records, following minor league baseball, and cycling.
Discussion Comments
By OeKc05 — On Aug 28, 2011

Almost all hotels use the electronic card scanner system these days. I only know of one that still hands out skeleton keys to its guests, and this is the type I actually prefer.

Card scanners are fine, until the electricity goes out. My husband and I had gone to the ocean on vacation, and we had a hotel room right on the beach. While we were out there at night, a big thunderstorm suddenly came up. We managed to make it into the building before the electricity went out, but we didn’t make it to our room.

The scanner would not work without electricity. We had to wait out in the hall for two hours. We were so tired, but we couldn’t sleep in the dark hall with people running around. Hotels really need to have key doorknob locks as backup for times like these.

By StarJo — On Aug 27, 2011

The office where I work has key doorknob locks. Only employees who have been there at least a year are given keys if they have to work overtime frequently. The boss has to trust you, or else he will stay there while you work, let you out, and lock up when you leave.

I got my key on my one-year anniversary of working there. The boss showed me the quirks in the door. He said that I would have to lift the knob a little while turning and then yank the key suddenly back to the left.

I couldn’t have gotten in the building without this tip. The defect in the doorknob offered extra security, because even if someone managed to get a copy of the key, they couldn’t enter without that knowledge.

By wavy58 — On Aug 27, 2011

My house has doorknobs that have twist locks, but they also allow you to use a key. These are the ones that open up to the outside.

I like being able to lock the door from the inside without having to use a bolt lock. The knob is designed so that even if you have twisted the small knob in the middle to the lock position, you can still turn the big knob to open the door without unlocking it.

This also means that it is easier to lock yourself out of your house by mistake. I did this a few times while getting use to the new knobs, but now, I have learned to always twist the knob from the outside before closing it. You can feel it stop short if the inner knob is locked.

By lighth0se33 — On Aug 26, 2011

Twist locks certainly came in useful for me when my mother babysat my five-year-old cousin. I would play with him for awhile, but he would get so hyper that he would hurt me at times, and I was bigger than him. So, I would run to my room and twist the lock to keep him out.

I always twisted the lock on the bathroom door when I was in there. My cousin had no idea that you weren’t supposed to walk in on a girl in the bathroom, so I used the lock to teach him this valuable life lesson.

By EdRick — On Aug 25, 2011

@Kat919 - I honestly don't know if those door knob locks are safe in case of a fire. They say that seat belts do not add anything to the time it would take to rescue you in a car accident, so I know some things that seem like they would add time really don't.

In a lot of places, you can call the fire department's non-emergency number to get advice on that kind of thing. Sometimes they will even send someone to your house to go over your fire escape plan. (And if you don't have one, you really should.)

You don't say how old your daughter is, but sometimes consistent parenting will solve the leaving-the-room problem. With my son, we just put him back to bed without speaking to him, always in exactly the same way, and it eventually worked. This, too, shall pass!

By Kat919 — On Aug 25, 2011

I'm curious about the last kind of door knob lock, the kind you use to keep kids out of a room. The only ones I've seen are plastic ones that fit around the knob. You have to squeeze it in a special way to be able to turn the knob.

But I can't see what use those would be with a tenant who hadn't paid rent. I haven't heard of putting a lock over a door knob; I'm imagining something like one of those "boots" they put on a car's wheel so you can't drive it!

Those plastic knob covers seem kind of useless; I hear that kids can defeat them almost as soon as they can reach them. Kids are like the Borg from Star Trek - they adapt quickly to all your new "weapons"!

The kind of lock the article is talking about seems like it would be more secure. But is it safe in case of a fire? I'm looking for a way to keep my daughter in her bedroom at night.

Malcolm Tatum
Malcolm Tatum
Malcolm Tatum, a former teleconferencing industry professional, followed his passion for trivia, research, and writing...
Learn more
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