The device, about the size of a toaster oven, sucked in ambient air and trapped airborne virus particles — if there were any to be found — in a specialized cartridge. Each afternoon, an employee would remove the cartridge and walk it to the UPS drop box across the street, sending it off for laboratory analysis.

Before the month was out, the air sampler had turned up traces of the virus. Officials ultimately traced it back to a town employee who had been working in the station, without a mask, during a quiet holiday period.

It was proof of concept for Thermo Fisher Scientific’s AerosolSense Sampler, which the company was making publicly available on Wednesday. The device, the company says, can be used to detect a variety of airborne pathogens, including the coronavirus. It could be deployed in hospitals, offices, schools and other buildings to monitor for signs of the virus as society begins to reopen.