Sigtronics pioneered the voice activated intercom market in 1974 and continues to deliver value and performance today in the 4 or 6 place FAA TSO approved SPA-400 / SPA-600 intercom series. With fail safe features that allow pilots to always hear the radio even if the intercom is off, and radio priority that assures ATC only hears the crew member transmitting, the SPA intercom series is the standard by which all others are judged.