A drug interlock for vehicles based on exhaled breath directed onto said SERS-active substrate, wherein a detected drug substance in exhaled breath of a subject locks said vehicle from use for at least a pre-determined time or a repeated exhaled breath test where no drugs are detected. A collecting surface has a Surface Enhanced Raman Spectroscopy (SERS)-active layer that comprises at least one SERS-active material. The collecting surface is arranged as an outer surface of a waveguide for contact with exhaled breath, such that at least traces of said at least one drug substance in said exhaled breath can contact said SERS-active layer for read-out of a Raman shift spectrum that is detected in-situ for said detecting the presence or determining the quantitative amount of said at least one drug substance from said exhaled breath.
