Thumbturn cylinders: safer exit or easier break in?
A thumbturn cylinder is a euro cylinder with a key on the outside and a small knob on the inside, so the door locks and unlocks from within without a key; in Dutch it is called a knopcilinder.
Turn the little knob and you are out. No searching for keys, no key left in the lock that blocks yours from outside. The thumbturn cylinder is popular in Amsterdam for good reasons. It also has one drawback that burglars know better than most residents.
What a thumbturn does for you
- You can always get out, even without the key. For a flat with children or an escape route this is a real safety advantage.
- A key left in the lock inside no longer blocks the key from outside, because there is no key inside.
- Locking up at night is one quick turn instead of a key you have to find and store again.
Where the risk comes from
A knob that opens the lock without a key is useful to anyone who can reach it. A letterbox in the door gives a hook direct access to the knob. A pane of glass next to the door can be broken so an arm fits through. Once the knob is reached, the door opens from inside, no lock picking needed.
Which doors should not have one
A thumbturn cylinder is a poor choice on any outside door with a letter slot, with glass within arm’s reach of the lock, or with a window beside it that can be broken. That covers many Amsterdam front doors and back doors with a glazed panel. On those doors a cylinder with a key on both sides is the safer option, with a spare key inside, out of reach of the letterbox.
Alternatives that keep the convenience
- A double cylinder with a key inside and a key hook at a safe distance from the door: the standard answer for a front door with a letterbox.
- A thumbturn with a locking function, where the knob only turns after a key or a button releases it, so a hook through the letterbox achieves nothing.
Whichever option you choose, the cylinder should sit flush behind a security plate and have anti snap protection. The lock security page lists the combinations.
What we do
Locksmith Amsterdam looks at the door, the letterbox and the glass together and tells you whether a thumbturn is a feature or a risk on your door. If it needs to go, our lock replacement service fits a double cylinder or a locking thumbturn in the same size, with the price confirmed before we start.
Frequently asked questions
What is a thumbturn cylinder?
A euro cylinder with a key on the outside and a knob on the inside, so the door locks and unlocks from within without a key. In Dutch: knopcilinder.
Is a thumbturn cylinder safe on a front door?
Only if the knob cannot be reached from outside. With a letterbox or glass next to the door, it is a burglary risk.
Can a thumbturn be opened through the letterbox?
Yes. A hook or wire through the slot can turn the knob and open the door. That is the main reason to avoid it on doors with a letter slot.
What is the alternative for a door with a letterbox?
A cylinder with a key on both sides, with a spare key inside out of reach of the slot, or a thumbturn with a locking function.
Can Locksmith Amsterdam replace my thumbturn cylinder?
Yes. Call +31 (0)20 210 1986 and we fit a matching double cylinder or locking thumbturn, with the price confirmed before we start.
Not sure whether your thumbturn is a risk? Call Locksmith Amsterdam on +31 (0)20 210 1986. We check the door, the letterbox and the glass on site and confirm the price before we start.
