Window alarm that permits partial opening - exist or make - and how?

22 Mar 2021
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United Kingdom
uPVC outward-opening side hinged windows on ground floor. Would like to be able sleep with them open to say 100mm but an alarm sound if they are forced open (burglar) BEYOND this.

I can't find a product that does this. ...So maybe a normal door chain (that can be unhooked for daytime full window opening), and a self-contained normal window contact alarm - lashed together with velcro and cable ties??? The velcro connection would give way when the window is forced beyond the doorchain limit - and separate the two parts of the alarm contact.

I can't quite get my head around how to do this. Any ideas?

I though this product would do it all-in-one:
...but I think it's just a normal alarm-on-opening combined with a restrictor - and the company never replied to my email enquiry.

So maybe a:
Door chain:
Combined with
A self contained alarm e.g.:
(or contact sensors as part of an alarm system like Ring dot com)

Any thoughts? It's for my elderly mother so the idea of a door chain is attractive as easy to use/release for less nimble fingers, and the alarm could stay on the whole time even while permitting full daytime window opening.
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