Bluetooth Drive Link is one tiny app that will manage your phone's bluetooth state for you, enabling it while you are driving your vehicle and disabling it when you turn off and leave it.
This will preserve your phone's battery life, allowing you to use your bluetooth hands-free loudspeakers or headset avoiding to forget the bluetooth radio on.
It's simple as that, you don't need to do anything except to pair you phone to your bluetooth device (if you haven't done that already).

Since there are a lot of different Android phones and bluetooth devices and the activity recognition may not work as expected in your configuration set, you should first install is DEMO version of the application to allow you to test the compatibility with your device and if the app functionality suits your needs.
You can find the free version searching for "Buetooth Drive Link (DEMO)" or by opening the following link:
https://play.google.com/store/apps/details?id=com.ferfig.bluetoothdrivelinkdemo

REQUIREMENTS:
· You need to pair your phone with your hands-free/headset bluetooth device (if you haven't done that already).
· You need to have the location services active on your device ("access to my location" active - it is not needed to activate the GPS).

RECOMMENDATIONS:
Before your phone connects to your bluetooth hands-free/headset device, leave it still while you start driving. If you pick up your phone and keep or hold it in your hands you will be sending erroneous data to the phone and will be very difficult to recognize the driving activity.

The app uses Google API's to detect in vehicle movement with low power consumption sensors and will run on android devices with Android version 2.2 and up.

The main purpose of this application/tool is the one described above; however it is not exclusive to handsfree bluetooth loudspeakers, it can also be used with any other bluetooth headset, working in the same way.

Please note that the app is recent and I'm still working in some improvements and for that I would like you to contact me first by e-mail to ferfig.apps@gmail.com if you have any suggestion or found any error/bug before rating or comment the app here at Google Play.
I thank you for that!
Thanks,
Fernando Figueiredo