Good old roller shutter security

Hello dear forum,

some time ago we moved into a house from the 80s. On (unfortunately only) one roller shutter, an old lift-up lock is installed. But I can't find this type anywhere, neither in the hardware store nor online. It is a quite ordinary plastic roller shutter with ventilation slots and a normal strap (but electric). I am not looking for one of those Schellenberg locks that is screwed into the wood at the top. Instead:

- a metal piece is screwed onto two slats
- the two metal pieces are connected by a kind of chain
- this "chain" runs inside the guide rail
- when lifting up, it stretches and allows lifting
- when pushing up, it dips and hooks into the guide rail
(>>> nothing is screwed onto the door frame or in the guide)
What is this type of lock called?
I would be very grateful for tips and links!

PS: Yes, I also think that this lock does not promise high security, but the common lock is too thick for us, and primarily I am concerned about deterrence. Also, at least I cannot lift that one roller shutter up...

Regards
Peter