sniffer
n.— «As they talk, the flashlight—this is no ordinary flashlight—is on the job. It is a little-known device that surreptitiously traps a sample of a motorist’s breath and tests for the presence of alcohol. Commonly called “sniffers,” they are used by some law enforcement agencies in the central San Joaquin Valley.» —“Sniffing out crime” by Tim Eberly Fresno Bee (California) Dec. 31, 2006. (source: Double-Tongued Dictionary)
Further reading
A listener named Tami contacted the show by WhatsApp to say that whenever someone would be talking about a subject that nobody else knew anything about, her father-in-law would respond with I had one of those, but the wheels came off. This is part...
When a musician is woodshedding a passage of music, they’re trying to master that part by repeatedly practicing it in private, as if having retreated to do so in a woodshed, away from others who might be bothered by it. This is part of a complete...
“Sniffer” also occurs in industry for a similar instrument used in leak detection. It’s often modified: “helium sniffer,” etc.