The Hi-Lo warning sound is a distinct tone that differs from a standard police siren and alternates between high and low frequencies. The tool is exclusively used by public safety agencies during natural disasters — including flash floods, wildfires, and levee or dam breaches — and other widespread public safety hazards to alert the public to evacuate.
All newly deployed Sacramento police patrol vehicles will be equipped with the Hi-Lo warning sound feature going forward, the department said.
“The Hi-Lo warning sound is not a replacement for existing emergency communication channels,” a department spokesperson said in a statement. “Instead, the warning sound provides an added layer of redundancy, ensuring residents receive critical evacuation notifications even if other tools or technology fail.”
The department said current emergency notification systems rely on cellular devices, radio signals, electrical connectivity and power, all of which can be disrupted by heavy smoke, power outages or damage to communication infrastructure during an emergency.
The Hi-Lo warning sound will provide an additional alert mechanism and will be used only when all people within hearing range are intended recipients of an emergency warning, the department said.
California authorized emergency vehicles to use the Hi-Lo warning sound for evacuation notifications under Senate Bill 909, signed into law in 2020. The warning tone, according to the Governor’s Office of Emergency Services , is intended solely to notify the public of an immediate need to evacuate and is part of a statewide evacuation alert system.
The system also can be paired with pre-recorded evacuation messages broadcast over a vehicle’s speaker system, according to Cal OES training materials. Those messages can be programmed in multiple languages.
About a dozen operational patrol vehicles in Sacramento’s fleet are already equipped with the Hi-Lo warning sound. All existing vehicles without the feature will be gradually phased out and replaced until the entire patrol fleet is equipped with the warning system, a department spokesperson confirmed.
Sacramento residents can hear the Hi-Lo warning sound in action and familiarize themselves with emergency evacuation procedures through a video posted on the department’s YouTube page.
©2026 The Sacramento Bee. Distributed by Tribune Content Agency, LLC.
