First, ensure you had followed this step:
Then open Chorme: enter chrome://flags
This will help owner Dashboard page become NEVER-IDLE page even when you leave this page inactive even for several days (only if you don't shutdown or let your computer sleep). 100% your police sound will work!
This Works in Pc perfect. But If some one using in Mobile is it possible to do the same setting to get the notification when the mobile screen off .
Any tips for mobile chrome while lock screen
waiyan the best is a native app, you will give specific permission and avoid these inconveniences