Wheaton residents heard tornado sirens for the second time in four days on Friday, Aug. 21, and for the second time there was no tornado.

The outdoor warning sirens sounded just before 10 a.m. due to another error by DU-COMM, the DuPage County dispatch agency that controls the system, according to the City of Wheaton. Officials in Villa Park and Addison also warned residents the activation was accidental.

The first false alarm hit at 3 a.m. Tuesday, Aug. 18, when a DU-COMM staff member triggered the sirens countywide while running what was supposed to be a silent technology check. DU-COMM said the staffer "accidentally activated the sirens" during the test and shut them off as soon as the mistake was realized, according to Fox 32 Chicago.

Friday's activation was different. DU-COMM told CBS News Chicago the siren was "not part of a planned test" and said the incident is under investigation.

No root cause has been disclosed.

"We understand erroneous activations can undermine public trust in the warning system," DU-COMM Deputy Director Tyler Benjamin told CBS News Chicago on Aug. 21. He urged residents to still take shelter and check a news source whenever they hear a siren.

The back-to-back mistakes have drawn sharp criticism. Villa Park Trustee Jorge Cordova told CBS News Chicago that two false alarms in less than a week is more than an inconvenience: "These are emergency warning systems that residents need to be able to trust."

Villa Park resident Danielle Guerrero told the station she chose to ignore Friday's siren because it was the second false alarm in four days. "If that was a real siren and there was a real storm, how many others are having that same train of thought?" she said.

DU-COMM, based in Lombard, provides 9-1-1 dispatch for municipalities across DuPage County. The agency upgraded its siren technology in May 2025 with systems that activate warnings faster during severe weather. Executive Director Jessica Robb has not publicly addressed the two incidents.

DU-COMM normally tests tornado sirens on the first Tuesday of each month at 10 a.m. Neither of the recent activations fell during a scheduled test window.

The agency has not announced a timeline for completing its investigation or what steps it will take to prevent a third false alarm. Residents who hear sirens should take shelter and verify conditions through the National Weather Service or a local news source.