A hacker, or group of hackers, has set off all 156 tornado sirens in the city of Dallas, Texas, on the night between Friday and Saturday, April 7 and 8. The alarms started shortly before midnight, at around 11:45 PM, local time, and were heard in twelve waves, before authorities shut down the entire system at around 01:20 AM. Officials said they kept stopping the alarms, but the intruder kept restarting the sirens. The sirens have been used primarily for warning the population against tornadoes.
Source: https://www.bleepingcomputer.com/news/security/hacker-sets-off-all-tornado-sirens-in-the-city-of-dallas-in-the-middle-of-the-night/