I have noticed this in the older version and latest iphone Waze app.
The Waze app is running in the background but the screen is black on my iphone (locked).
I always leave my display off to converse battery.

I see a police trap and know it is reported on waze, the MOMENT I turn my display on and waze reopens the phone speaker says POLICE ALERT AHEAD and i get the popup to press thumbs up, etc.

I know I have heard alerts before, and also spoken directions before (am in alerts only mode now)..
but do i HAVE to leave my iphone display on LIVE and visually have it open to get these alerts?
I do have it in navigation mode to my destination and i have event radius set to ON ROUTE.

I would love to get alerts without the display being on live to save battery, but I can leave it on and have the autolock feature toggle to make the phone not black out the display if this is needed.

I usually rely on the speaker telling me of the alert (like trapster does) even with the display off,
and thought Waze worked this way in the past, but just wanted to make sure of what mode I should leave my phone in (display on/off) to hear the alerts in TIME, in the future.

I had almost driven past the alerts (there were 3 in one area with 3 people reporting it a bit off by seconds driving), and I would really like to know about these before the alert is in site (like 1 mile away etc.) I think it is just me turning the display on and the program waking up that is reporting the alerts when i view the screen again. Am I wrong?