We have a tablet that we put in a headrest mount for the kids to watch on longer journeys. In the past I attached an FM transmitter so that audio could be fed through the car stereo, and I could control the volume from the dash. The only problem with that was local radio stations in other regions stomping over the FM signal I’d pre-set earlier in the journey.
I bought the Bluetooth audio receiver from Justop. It’s the BTR006 model which apparently has some updated chipset. It’s about £15 on Amazon.
This tiny unit draws power from its built in li-on battery (or any USB port) and when fully charged will allow for 8-10 hours of use, and something like 250 hours of standby.
It was easy to pair up with my Samsung Galaxy S3, and Blackberry Playbook.. both of which will be using A2DP. The signal travels 5-10m without problems, but at extremes, the signal gets scrambled by walls/people. For my use, which is for in the car (tablet with the kids in the back) it works a treat.
The only thing I don’t particularly like is the tiny power socket which uses some non-standard plug instead of micro or mini USB. That’s a real pain when I have loads of micro USB-ended adapters kicking around.