I have all of our vehicles paired with my phone so I can stream music while driving. The problem is that I am not the only person to use them. So I am listening to something on my airpods and someone else starts a car and my phone automatically pairs with the car and plays over that. Is there a way to disable this other than forgetting the car when I am not using it?
iPhone XS
Unpair a Bluetooth accessory
To unpair a Bluetooth accessory, tap Settings > Bluetooth, find the device you want to unpair, and tap 
, then Forget this Device.
When you Forget this Device on your iPhone, iPad, or iPod touch, that accessory is removed from the list of available Bluetooth devices. To add the Bluetooth accessory to your device again, place it back in discovery mode and repeat the steps above to pair it again.
If you can't pair your Bluetooth accessory
If you're still unable to pair your Bluetooth accessory with your device, find out what to do.
Ok that's what I was afraid of. I wish there were an option to disable that like they have for wifi
Since there are multiple vehicles, you also should have the option in the vehicle's settings to set it up to give one device the option to be the first device to pair. I have my iPhone and my wife's iPhone paired to both of our vehicles. However, if we are both in her car, it will default connect to her car first, and if we are in my car, it pairs to me first. If we are in each individual car, it will pair to the person in the vehicle.
So there is no way to keep it from pairing other than removing it?
Correct. Once you pair them again they will auto connect per the Bluetooth standards.
Disable auto pair for Bluetooth devices
