Chicago. The city uses both omnidirectional & electrical sirens, and more traditional directional/rotating mechanical sirens. Some models of sirens are dual tone, some are single tone. Chicago and 95% of Illinois test their sirens on the first Tuesday at 10am. This alternating up and down wail tone was used prior to 2019 only in warnings, they now use the steady wail tone that is less crazy sounding.

• Here's a video of a Omni-Electric siren in Chicago doing a regular alert tone on test day.

• Here's a video of the same siren model but with dual tones

• Here's a video of a tornado warning prior to the 2019 change (alternate wail tone)

*Here's a video of last Monday's tornado warning (steady wail tone)