Last summer we had a run of returns from a German buyer. The complaint was that the motion-sensor headlamps would flick on by themselves, sometimes in a backpack, sometimes just sitting on a shelf. Annoying, and it kills the battery overnight.
My first guess was the sensor was just too sensitive. We turned the threshold down and tested. Still happened, just less often. So that wasn't the whole story.
What we eventually found was the IR sensor was picking up its own heat. When the torch ran on high for a while, the front housing warmed up, the air in front of the lens shifted, and the sensor read that as a hand wave. Classic. The fix was partly software, adding a short lockout after the lamp turns off so it ignores movement for a second or two, and partly moving the sensor window a couple mm away from the LED heat.
We also added a simple gate: the sensor only arms when ambient light is below a level. No point having a hands-free torch trigger in daylight anyway. That alone cut the false ons in storage by a lot, because most cupboards aren't pitch black during the day.
The bit that embarrassed me is that one of our own assemblers had flagged this months earlier. She said the units on her bench kept lighting up and she assumed she was bumping the table. We brushed it off. Lesson learned, the people on the line see the problem first.
After the change we sent the German buyer a fresh batch and asked them to leave a few in a warm car for a week as a torture test. No false triggers reported. We now run that same warm-soak test on every sensor model before it ships.
