A auto-injector device having a housing (212, 214), a cartridge for containing a medicament, a first needle tip (230) arranged to penetrate said cartridge, a second needle tip (230) for injecting said medicament into a target, said first and second needle tips being in fluid communication, a plunger rod (242) to move said cartridge so as to be pierced by said first needle tip, said plunger rod (242) having a recess (270) in an end thereof, the improvement comprising a battery (258), a printed circuit board (250) electrically communicating with said battery, an electrically conductive element (274) having a first end in electric communication with said battery (258) and printed circuit board (250), a second end within said recess (270) in said plunger rod (242), said second end being electrically insulated, a coil spring (246) surrounding said electrically conductive element and being spaced therefrom, the arrangement being such that when said plunger rod (242) is activated, said second end of said electrically conductive element is released from said recess (270) in said plunger rod (242) and contacts said coil spring (246) to complete an electric circuit.