Ends 1/23 at 10PM PT. Electronics.woot! has the refurbished Amazon Smart Air Quality Monitor on sale for $40 - 20% off with coupon code DEVICES20 [Exp 1/23] = $32 with free shipping with Amazon Prime, otherwise $6.

Tracks 5 metrics: particulate matter (PM 2.5), volatile organic compounds (VOCs), carbon monoxide (CO), humidity, and temperature. Sends alerts to phone / Echo devices.