A two-part electrotransport drug delivery device (20) is comprised of a controller (22) which has a plurality of different electronic outputs. The controller (22) is adapted to be mechanically and electrically coupled to a plurality of different drug-containing units (24). Each drug unit (24) includes a means (40, 42, Rx, Cx) for signaling the controller (22). The signal is read by the controller (22) and a predetermined electronic output is thereby selected and applied through the drug unit (24) in order to deliver the drug contained therein by electrotransport. The signal sent by the drug unit (24) to the controller (22) may be an optical signal (e.g., reflected light), a signal sent by an electro-mechanical connector, an electrical signal (e.g., resistance or capacitance), a magnetic signal or a metal detector sensing signal.