A hyperwave signal interceptor (HSI) was a sensor that detected the telltale fluctuations in the local hyperspace field that resulted whenever a starship entered or exited hyperspace. They could not indicate the origin or destination of a ship, but could record its entry or departure, as well as its mass and speed. Hyperspace signal interceptors were also capable of tapping into hyperspace based transmissions, such as those broadcast by the HoloNet and Hyperradios, as well as communications through subspace.