An FM transmitter with a Bluetooth car charger is a multifunctional device that allows you to play audio from your phone or other Bluetooth-enabled devices through your car's FM radio. It also serves as a car charger to keep your devices powered while driving.

Here's how it typically works:

1. Bluetooth Connectivity: The device connects to your phone or other Bluetooth-enabled devices wirelessly. Once paired, you can stream audio from your device to the FM transmitter.

2. FM Transmission: The FM transmitter converts the audio signal from your phone into an FM radio frequency. You can then tune your car's FM radio to the specific frequency set by the transmitter to hear the audio playback.

3. Car Charging: The FM transmitter also features one or more USB ports that allow you to charge your devices while using the transmitter. This way, you can keep your phone or other gadgets charged during your car journey.

4. Hands-Free Calling: Many FM transmitters with Bluetooth car chargers also come with a built-in microphone, allowing you to make and receive hands-free phone calls while driving.

5. Control: Some FM transmitters have physical buttons or dials to control functions like volume, playback, and phone call management. Others may have touch controls or be controlled through a mobile app.

FM transmitters with Bluetooth car chargers are popular accessories, especially for older cars without built-in Bluetooth connectivity or auxiliary input. They provide a convenient and affordable way to enjoy your favorite music or podcasts while driving, and they also help keep your devices charged and ready to use. However, the audio quality may vary depending on the FM transmitter's signal strength and the FM radio's quality in your car. It's a good idea to read reviews and choose a reputable brand to ensure a better audio experience.