Outdoor warning sirens, commonly thought of as "tornado sirens," are customarily activated when a tornado warning is issued for the immediate area. This means a tornado has been sighted within DuPage County or an adjoining area and is potentially tracking toward Wheaton.
If you hear the outdoor warning siren, take immediate action. Seek shelter immediately in the lowest level of a building (preferably a basement, if there is one).
As a reminder, the City of Wheaton tests its warning system at 10 a.m. on the first Tuesday of every month.