Thank you JD for your comments and advice.
I might for fun take a cheap pir sensor apart and see if I can somehow glue or mount a different lens on the front. This is quite tricky as its’ hard to see what Pyro has been used and therefore know how far away to mount the lens. Fortunately the cheap sensors tend to be simple dual element Pyros which makes things easier.
The biggest challenge is making them waterproof (I want to mount outside) as the HDPE the lenses are made from is a pig to bond anything to. The best way is to clamp the lens and this might mean investing in a 3D printer and come up with a mechanical design. Another big project …
That’s why I was hoping to find something already in the market.
BTW, you can botch it by blanking off segments on an existing lens in a similar way to using zones in the camera versions. A marker pen will do. Better do it on the inside of the lens as the ink will eventually come away from the HDPE plastic. The best way is to use a metal foil if you can fix it over the lens segments that you don’t want to be active.
There are sensors out there with little shutters you can slide across the lens to block off some unneeded segments.
I would still prefer an off the shelf solution…