Abstract: Multiple gas lift valves interposed in a well tubing string are each configured to have gas flow ports adapted to emit a predetermined acoustic signal for transmission through the well to a microphone or similar acoustic signal receiver whereby a determination may be made of which gas lift valves are open or operating properly. One or more of the gas lift valves may also include fluid pressure, temperature and viscosity sensors as well as a valve opening sensor and/or valve pressure setting control and an associated signal controller/generator arrangement for generating signals for transmission to the surface. The signal generators may be of the acoustic or so-called stress wave type.