Should PIR sensors be placed facing away from a window to avoid false
triggering?
You should put them on the opposite wall to avoid false triggering by
rustling curtains. Place them in a corner so that they face across the
window, not directly at it. A PIR is most sensitive when an intruder
moves across it rather than toward it. For more reliable triggering,
I'd suggest a dual sensor, ie one that combines a PIR and a microwave
detector. The latter is insensitive to heat variations.
- Franc Zabkar