* frying indoors generally swiftly puts things in the unsafe range. Especially if it led to browning.
* a neighbour's bbq would do the same if the window was open
* idling truck on the street for construction? Unsafe range
* surprisingly, the toaster would raise levels if it was on high enough to brown toast
Really helped me make better decisions about when to open/shut windows and how to cook.
I got the laseregg after reading reviews of air quality monitors used in china. Apparently it holds up well to specialized lab sensors. It has a battery and can be moved around