A microphone (102, 300) comprising: a microelectromechanical system (MEMS) circuit configured to convert a voice signal into an electrical signal; an integrated circuit (304, 400) coupled to the MEMS circuit, the integrated circuit (304, 400) including an oscillator and a voice activity detector that determines whether voice activity is present in data representative of the electrical signal; the integrated circuit (304, 400) clocked by an internal clock signal based on the oscillator when the voice activity detector determines whether voice activity is present during operation of the microphone (102, 300) in a voice activity detection mode; the integrated circuit (304, 400) includes a buffer in which the data representative of the electrical signal is buffered; the integrated circuit (304, 400) configured to provide an interrupt signal to an external-device interface after detection of voice activity in the data; the integrated circuit (304, 400) configured to operate in a mode controlled by an external clock signal received at the external-device interface in response to the interrupt signal; the external clock signal being effective to cause the microphone (102, 300) to operate in a full system operation mode during a second time period, the microphone (102, 300) configured to operate in the voice activity detection mode during a first time period in absence of the external clock signal, the voice activity detection mode having a first power consumption and the full system operation mode having a second power consumption, the first power consumption being less than the second power consumption. a microelectromechanical system (MEMS) circuit configured to convert a voice signal into an electrical signal; an integrated circuit (304, 400) coupled to the MEMS circuit, the integrated circuit (304, 400) including an oscillator and a voice activity detector that determines whether voice activity is present in data representative of the electrical signal; the integrated circuit (304, 400) clocked by an internal clock signal based on the oscillator when the voice activity detector determines whether voice activity is present during operation of the microphone (102, 300) in a voice activity detection mode; the integrated circuit (304, 400) includes a buffer in which the data representative of the electrical signal is buffered; the integrated circuit (304, 400) configured to provide an interrupt signal to an external-device interface after detection of voice activity in the data; the integrated circuit (304, 400) configured to operate in a mode controlled by an external clock signal received at the external-device interface in response to the interrupt signal; the external clock signal being effective to cause the microphone (102, 300) to operate in a full system operation mode during a second time period, the microphone (102, 300) configured to operate in the voice activity detection mode during a first time period in absence of the external clock signal, the voice activity detection mode having a first power consumption and the full system operation mode having a second power consumption, the first power consumption being less than the second power consumption.