A speech processor unit (12) for a cochlear implant system. The speech processor unit (12) comprises a signal processor for processing incoming auditory signals and for forwarding processed signals to an implanted component (18) of the system, a monitoring means for monitoring a predetermined parameter, and a controller, controlled by the signal processor, for placing the unit in an idle state in the absence of the parameter. The predetermined parameter can comprise the presence or absence of the implanted receiver antenna coil (22) relative to the external antenna coil (16). The invention allows the speech processor unit (12) to be supplied without a physical on and off switch.