An apparatus includes a housing. The housing includes a concentrator and a plurality of signal acquisition devices. Each signal acquisition device is coupled to a respective sensor. Each sensor measures an environmental parameter outside the housing. Each signal acquisition device includes an acoustic transducer. Each signal acquisition device includes a controller to accept measurements from the respective sensor, process the measurements and format them into a transmittable form, and transmit the formatted measurements via the acoustic transducer. A concentrator includes an acoustic transducer to receive acoustic transmissions from the plurality of signal acquisition devices, a processor to process the received acoustic transmissions, and a telemetry device through which the processor can transmit the processed transmissions.