Beginning in 1957 the United States government required that any radio transmitter have the means of monitoring for a Conelrad alert and stop transmitting if one was in progress. The fear was that Soviet guided missiles could use the transmitted signal as a homing beacon.

Heathkit produced the CA-1, which monitored a broadcast station and alerted the amateur radio operator of any interruption. When properly connected and operating the CA-1 would prevent any accidental transmissions during a Soviet nuclear attack.

Conelrad (CONtrol of ELectronic RADiation) was replaced in the early 1960s with the Emergency Broadcast System (EBS), which dropped the requirement for such transmitters to go off the air.