Story highlights All 156 emergency sirens went off around 11:40 p.m. in what appears to be a hacking incident, city says

The city's emergency alarm system is expected to be back up and running by Sunday

(CNN) Dallas residents were jolted out of bed late Friday evening after a hacker triggered all the city's emergency sirens, setting off a wave of panic and confusion.

All 156 emergency sirens were activated around 11:40 p.m. in what appeared to be a hacking incident that "woke up a lot of people," Sana Syed, managing director of public information for the city of Dallas, said at a news conference on Saturday.

The Office of Emergency Management was able to turn off all the sirens by 1:20 a.m., said Syed.

"It does appear at this time it was a hack, and it does appear this came from the Dallas area," she said.

As the sirens blared, frightened residents called emergency services and took to social media to voice concern and learn what had happened.

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