Here is how the radar works:
When Garmin RTL 510 is paired to a Garmin bike computer (in my case its with Garmin Edge 1030) a small icon appears in the upper right corner of the screen. It is visible in every mode. This way a car can’t sneak up on you while you change settings.
When the radar detects a car approaching (only from behind) it displays a small strip on the right or left side of the screen (configurable). The strip shows each car as a dot moving closer to a stationary dot at the top of the screen, which represents you.
Depending on how fast the car is approaching relatively to your current speed the sides of the screen show a slight orange or red glow. It is very subtle, but effective. Orange for incoming. Red - incoming fast!
Once the last car passes, the radar takes a second to confirm that there aren’t any more cars and glows green. The road is clear so the strip with dots disappear. As soon as it detects another incoming car, the strip with dots shows up again and the process repeats.
What about audible alerts of incoming cars? Yes, there are 2 styles of alerts: single-beep and multi-beep. On busy roads I turn off audible alerts, but on rural roads I turn on multi-beep, which is nice and loud.