My flat has a pair of these attached to every window frame, opposite each other. They have no visible branding on them.


Does anyone have any idea what they are for?

  • Does something interesting happen when you pull or push the handle in any of the five available directions? Perhaps a ventilation slot opens? Maybe something more exciting like the zombie-shutters drop down? May 21, 2017 at 22:29
  • Each window has two of these, one on each side, right? Trying pulling down or pushing up on the tabs on both sides simultaneously. May 22, 2017 at 0:29
  • The plate that the handle type thing is attached to pivots on the vertical axis. On the other side of that plate is a kind of foam backing. Other than that, the handle doesn't move. The things opposite each other aren't attached in any way. Pulling on them at the same time would have no effect. If no one knows what this is, I'll unscrew one from the window to see if there are any more clues to its function.
    – MJeffryes
    May 22, 2017 at 8:42

1 Answer 1


I removed one of these devices, and behind it I found two voids in the frame leading to some more foam. I believe that these are "trickle vents", which are required in UK building regulations. In a modern, well insulated house, there is little exchange of air with the outside, which can cause moisture to build up in the air leading to condensation and damp. Trickle vents are intended to prevent this from happening. The protruding thing in the middle of the vent pictured allows the vent to be sealed shut.

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