FM Transmitter — Under $20 An FM transmitter plugs into your cigarette lighter socket and connects to your device via an aux cord or Bluetooth. The transmitter broadcasts whats playing from your phone over a short FM frequency to which you tune your cars radio and receive.

How can I add Bluetooth to my car Aux?

0:122:043 Ways to Add Bluetooth to any car - YouTubeYouTube

How do I connect my phone to my Aux in my car?

Auxiliary: Connect the AUX cable directly to the headphone jack on your phone. If your phone does not have a headphone jack, connect a USB-C headphone adapter to it. Then, connect the other end of the cable to the AUX IN port on your car stereo.