There is disclosed a transdermal analyte sensor device. The device includes a sensor cartridge having a membrane permeable to a target analyte transdermally received from a subject, a reservoir containing a fluid to receive the target analyte through the membrane and an enzyme to react with the target analyte to form a byproduct, a working electrode to generate an electrical current based on a concentration of a byproduct, and a cartridge electrical contact to transmit the electrical current. The device also includes a device body having a device electrical contact to receive the electrical current from the cartridge electrical contact, a transmitter to transmit a signal based on the electrical current to a monitoring device, and a cartridge receptacle to receive the sensor cartridge and position the membrane to contact skin of the subject.