Pirate radio: Signal spoof set off Dallas emergency sirens, not
network hack
By Sean Gallagher
Published: 2017-04-12 · Archived: 2026-04-06 03:19:37 UTC
Broadnax said that measures had been taken to prevent the incident from happening again, but he would not say
what those measures were.
Alert sirens, especially older ones like those used in Dallas, are usually controlled by tone combinations used by
the Emergency Alert System broadcast over the National Weather Service’s weather radio. Alternatively, they can
also be controlled by Dual-Tone Multi-Frequency (DTMF) or Audio Frequency Shift Keying (AFSK) encoded
commands from a dispatcher or command center terminal sent over UHF radio frequencies that were set aside for
emergency agencies’ use by the FCC in 2004 (these are typically in the 700 MHz range).
If the frequency used by the sirens in Dallas for DTMF or AFSK wasn’t monitored, an attacker could conceivably
broadcast an endless number of guesses at DTMF or AFSK encoded commands until the sirens were set off—and
then just play that command signal repeatedly. But it’s possible that someone managed to gain access to
documentation for the siren system and knew exactly which commands to send.
Source: https://arstechnica.com/information-technology/2017/04/dallas-siren-hack-used-radio-signals-to-spoof-alarm-says-city-manager/
https://arstechnica.com/information-technology/2017/04/dallas-siren-hack-used-radio-signals-to-spoof-alarm-says-city-manager/
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