Ultraphone

Amalfi wondered if the Hruntans understood English; not that he was worried about the present interchange being overheard—the giant planet would block that most effectively, since the Utopians used ordinary radio rather than ultraphones or Dirac communicators—but it was of the utmost importance, if Hazleton's scheme was to be made workable, that the Hruntans should have heard and understood the warning the Earth police had issued to the city.