A method and a system for ultra-low-power acoustic sensor including a buffer transistor, which gate terminal is connected to a first terminal of a capacitive acoustic sensor, which drain terminal is connected via a load network to a power source and to an output terminal, and which source terminal is connected to the regulated current source, where the regulated current source is connected between the source terminal of the buffer transistor and a reference terminal, and where the reference terminal being connectable to a second terminal of the capacitive acoustic sensor.