Breathalyzers detect alcohol via:
Cr2O72- + C2H5OH → Cr3+ + CH3CHO
Ethanol - reductant; no oxidant
Ethanol - reductant; Cr2O72- - oxidant
Ethanol - oxidant; Cr3+ - reductant
Ethanol - reductant; Cr3+ - oxidant
Ethanol - reductant; Cr2O72- - oxidant