I'm looking for sensor options for proximity detection through a pane of glass. Something that will sit 6-24" on one side of a pane of glass, and be able to detect presence the same (roughly) distance on the other? I assume ultrasound won't work, but am not sure about infrared. If not, are there other options?
Edit per this link from the comments, most glass is opaque to IR, so no, it won't work. That leaves the second part of the question - are there ways to detect presence / motion on the other side of a pane of glass. Video-based motion detection won't work because I need to be able to restrict distance (i.e. something present/moving within a fairly tight distance of the glass). Use case is something along the lines of a home security motion sensor looking out the window.