With battery left (in hour) and number of cars that have doubled me, next step : audio alert on the phone ; that part will need an android app i think, we'll see
Actually testing some development around the Radar :
https://www.youtube.com/watch?v=676KHLb9Rus
If you're hearing impaired then I think you can configure the mobile app for a vibration alert. Or if you also have a Garmin watch you can connect the Varia radar sensor to that and it will vibrate on your wrist.