A microphone apparatus including a MEMS transducer, an acoustic activity detector, a local oscillator, and an external-device interface standardized for compatibility with devices from different manufacturers is disclosed. The microphone apparatus has a first mode of operation during which the apparatus is clocked by the internal clock signal when the acoustic activity detector processes digital data for acoustic activity, and a second mode of operation during which the microphone apparatus is clocked by an external clock signal received at the external-device interface after voice activity is detected by the acoustic activity detector.