Heising played a major role in the development of military radio telephone systems during World War I, and for transoceanic and ship-to-shore public communications. He also conducted research on ultra-short waves, electronics, and piezoelectric devices, and invented important modulation systems including the constant potential system, the grid modulation system, the rectifier modulation system used in carrier telephony, and the constant-current or Heising modulation system, which was standard on most early radio telephone transceivers.