An RDS function is automatically built into many of these FM transmitters. Essentially, this means that it will transfer useful information to the screen of your device including song title, artist’s name, caller ID etc. Many also come with an in-built voltmeter so that you can also check up on your car’s current battery levels. Since the screens are relatively small, they only have room to display a limited amount of information, but you don’t want too much as this could end up distracting you from your driving.