: A brief beep every few seconds on a channel to notify units that an emergency is in progress and the air should remain clear for priority traffic.
In P25 (Project 25) digital police radios, a “new message” tone is often an MDC1200 “Preamble” followed by a 1200 Hz burst. For analog systems, it is usually a DTMF ‘D’ tone or a proprietary sequence. No universal link exists; tones vary by manufacturer. police walkie talkie sound message tone link