Stop mounting motion sensors behind glass windows

I've been to three jobs this month where someone put a motion detector behind a window pane thinking it would work through the glass. It won't. Infrared can't penetrate glass at all, you're just wasting everyone's time. The worst one was in a Chicago office where they mounted four DSC units behind a storefront window and wondered why nothing triggered. Has anyone else run into installers doing this or am I the only one catching it?

2 comments

2 Comments

parker_campbell10d ago

Pulled a similar one myself back in 2019. Had a customer who insisted their PIRs would work through a sliding glass door. Took the time to show them with a multimeter and a heat lamp how it just reads the glass temperature instead. Swapped them to dual-tech units with surface mount brackets and it worked. Sometimes you gotta let them see the proof firsthand.

stone.evan9d ago

The heat lamp demo is a good visual, but a multimeter wouldn't really tell you much about what a PIR is seeing (you know, since they detect IR radiation, not voltage). Still, showing him the glass temp reading with an IR thermometer probably drove the point home way better.