Waterless electrochemical transdermal alcohol sensor. In one embodiment, the sensor includes a proton exchange membrane imbibed with an imbibing liquid that includes at least one cationic substance that is liquid at room temperature. As examples, the cationic substance may be one or more ionic liquids with an imidazolium, phosphonium, ammonium, pyridinium, pyrrolidinium, or sulfonium backbone structure. The imbibing of the proton exchange membrane with the cationic substance obviates the need for the periodic addition of water to the electrochemical cell. The sensor additionally includes a sensing electrode, which is bonded to one side of the proton exchange membrane, and a counter electrode and a reference electrode, both of which are bonded to the opposite side of the proton exchange membrane. The sensor may be incorporated into a wearable transdermal alcohol sensor device, which, in turn, may be incorporated into a system for detecting transdermal alcohol.