Emergency dispatchers received around 4,400 calls between 11:40 and 3:00 a.m. The city’s FBI office posted a tweet informing residents there was “no active emergency.” After investigation, it appears this was a hacking incident. It does appear at this time it was a hack, and it does appear this came from the Dallas area,” Sana Syed, managing director of public information for the city of Dallas, said at a news conference. Dallas Mayor Mike Rawlings has promised a full investigation. He described the incident as “an attack on our emergency notification system.” “We have notified the FCC for assistance in identifying the source of this hack. We are putting in safeguards to ensure this type of hack does not happen again,” the city said in a news release. Outdoor warning sirens are designed to alert people outside to go indoors for shelter and information.