I have upvc windows with the typical handle with push button and lock which rotates ninety degrees to engage/disengage the locking mechanism (3 bolts in the bottom of the window frame which engage with plates along the sill).

What I can’t work out is the actual purpose of the embedded lock in the handle (with key). When locked, it prevents the handle being used, and this might be useful for security from the inside (eg if a toddler is roaming about) but it doesn’t seem to increase the security vs an attack from the outside.

Am I right or am I missing something? Insurance companies seem to require these locks, I think, which suggests they have some purpose but I can’t see it.

One of my windows was recently levered open from the outside, which snapped the 3 plates on the sill. The embedded lock in the handle seems of no value to protect against this activity. Or am I being dumb?

  • I've not heard the term "up can window handle" before. Could you please provide a link or explanation of what this is?
    – psaxton
    Jul 30, 2020 at 5:22

1 Answer 1


The intent of the handle lock is that "break window, open handle so you don't have to climb through the jagged glass left in the frame, climb in opened window" is made difficult.

If the lock plates are too weak and snap when pried, that case gets no help from the handle lock.

Sad reality is that if a thief wants in, they will get in - "security" is just slowing them down or making things more difficult for them.

  • 2
    "Security" can also involve forcing them to make enough noise to wake the neighbors. +1 for this, but the lock is also useful for keeping younger children from opening the window and accidentally tipping themselves out of it as they enjoy the wonder of a 2nd story view.
    – FreeMan
    Jul 29, 2020 at 12:04
  • Ok that makes sense now, thanks.
    – dave
    Jul 29, 2020 at 12:41

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