The Boulder County Sheriff's Office is adding a patrol-vehicle Hi-Lo evacuation siren to its emergency alert and warning system [1].
This change aims to increase the effectiveness of public notifications during mandatory evacuations. As wildfire risks intensify in Colorado and other regions, officials are seeking ways to ensure residents recognize urgent warnings that differ from standard traffic-stopping sirens [2, 3].
In Colorado, the rollout is not limited to Boulder County. Clear Creek and Jefferson counties are also implementing these new evacuation alert sirens to help notify residents if wildfires spread [2]. The Hi-Lo sound is distinct from the traditional wail or yelp sounds used by police during routine stops or emergency responses.
Similar measures are being taken in California. The Sacramento Police Department is equipping new police vehicles with the same Hi-Lo sound to assist with emergency alerts [1, 3].
These sirens serve as a critical layer of a multi-modal warning system. While digital alerts and phone notifications provide immediate data, the physical sound of a patrol vehicle in a neighborhood provides a direct, audible signal that an immediate evacuation is required [2, 3].
“The Hi-Lo sound is distinct from the traditional wail or yelp sounds used by police.”
The adoption of Hi-Lo sirens represents a shift toward more specialized auditory signaling in public safety. By diversifying the sounds used by emergency vehicles, agencies can communicate specific instructions—such as an immediate evacuation order—without relying solely on digital infrastructure, which can fail during large-scale disasters like wildfires.
