Keyring design: It is portable, handy and convenience to carry. Only Green LED light on: Safe, the alcohol concentration level is under 0.02% BAC (0.1mg/l BRAC). Only Yellow LED light: Caution, the alcohol concentration level is 0.02% to 0.05%BAC (0.1mg/l BRAC to 0.25mg/l BRAC).
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