How to Stop Nest Protect From False Alarming (My $500 fail)

If i am not to remember wrong, it is actually inside the disc, which is actually a round chamber where the magic happens. A infrared light is emitted. Some mirrors inside are picking it up and reflecting it around. In the other side there is a receiver. When dust is detected inside the "chamber" the intensity of the light is weaker/interrupted by smoke or in your case dust particles, thus sounding the alarm. Sometimes sun rays can also disturb the signal, and cause a false alarm.

[@volcolby]

After tearing apart the inner assembly, (not on the video), your explanation makes sense. It is an empty cavity with air flow openings and then what could be a tiny laser light (hard to tell with the naked eye.)