From Wikipedia:
Radon (pronounced /ˈreɪdɒn/) is the chemical element that has the symbol Rn and atomic number 86. Radon is a colorless, odorless, naturally occurring, radioactive noble gas that is formed from the decay of radium. It is one of the heaviest substances that are gases under normal conditions and is considered to be a health hazard.
The device simply measures levels of Radon in your home (if there is any...i dunno anything about Radon)

Someone is lookin out for ya.

Did you have anyone doing any inspections or anything? It looks like a pricey piece of equipment that someone could get in trouble for losing.