Name that whiff

Chemicals ranging from nerve gas to emissions from mouldy food can now be
sniffed out by a palm-sized vapour detector made by by Orlando, Florida-based
Sawtek. The VaporLab system contains four piezoelectric crystals, each of which
is coated with a different polymer that absorbs target vapours. Absorption
changes the crystal’s resonant frequency, which is then matched to a database of
frequency shifts of up to 200 known compounds.