Thanks to a flaw in popular emergency alert systems, hackers with knowledge of radio frequencies could remotely hijack the system with as little as a laptop and a $35 two-way radio and activate the sirens, trigger false alarms or even broadcast any audio of their choosing.

The vulnerability, dubbed SirenJack, is in emergency alert systems manufactured by Acoustic Technology Inc, aka ATI Systems. It was discovered by security firm Bastille researcher Balint Seeber after he determined that the RF signals used in San Francisco’s emergency alert system were not encrypted; the activation commands were sent “in the clear.”

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