The siren functions at 12:00 as a way to test the functionality.
The siren is used very seldom as a backup notification for Emergency Services. When the siren is used for this it will cycle up and down for approximately 5 minutes before stopping.
The siren when signaling a possible Tornado will function for approximately 5 minutes as a warning and will function for approximately 1 minute when indicated to serve as an all clear signal. Both the Tornado warning and the all clear signal the siren will be constant without cycling.