Bacteria called methylotrophs can use methane and methanol as fuel; in doing so, they produce large amounts of formaldehyde during growth, but until recently no one knew how they detected and responded to this toxic compound. Publishing on 26th May, 2021 in the Open Access journal PLOS Biology, Christopher Marx of the University of Idaho and colleagues describe their discovery of a novel formaldehyde sensor in the bacterium Methylorubrum extorquens, and other methylotrophs.