We've been thinking about making the sensor portable so it can alert when it's time to mask up because its often hard to be sure if you're not being unnecessarily exposed.
The few days after that I had shortness of breath and trouble concentrating. It was pretty alarming. Not wearing a mask, which I had with me, was a big mistake.
I think your suggestion is excellent.
So portable monitor in my view is overkill, I just check AQI in the area and close windows and run air filter indoors and don't cycle when it's bad.
But if it's a really convenient monitor I'd not mind it! In my experience accurate monitors are not small and not cheap though...