Provided here are methods and system to detect an untethered device in a wellhead. The untethered device includes a housing, a transducer, and one or more sensors configured to measure data along the subterranean well. The transducer emits acoustic signals that are received by microphones on the surface of the wellhead. Based on these acoustic signals, the location of the untethered device is determined and appropriate valves may be opened or closed by an operator.