What proximity detection technologies can work through glass?
You could use a microwave presence sensor e.g. this one which mentions glass specifically
In general, they will work through glass, without a big reduction in range.
They are often combined with PIR detectors to reduce false triggering (from sources of heat), but usually configurable so you can only use the microwave part.
IR goes through glass if it’s anywhere near the visible region. Soda-lime glass:
