EG Air atmospheric quality monitor.  The thing is aggressively unbranded -- the device maker can be found in the menu, but there's no hint of a model number.  The model number in this listing comes from another listing, and I hate doing that, but it seemed better than not having one at all.  (And I don't want to take it apart, just on the off chance it's better-marked inside.)  This thing also looks identical to a bunch of other ones found for sale various places.

I kind of blame Amazon for this -- a mall of generic products, without branding, without even association with a storefront, made in the same factory and sold under a dozen forgettable names.  Even though it's commonplace, I feel like Amazon made the business model mainstream.

Anyway, the device detects particulate matter -- PM1, 2.5, and 10.  Also detects formaldehyde and provides a general VOC measurement.  Also has a thermometer and humidity sensor.  Charges via USB micro-B.  Battery seems in good condition, able to run the device with screen on for a while.

Original package and cable not included.