During the Google developers conference in May they announced they would be releasing a standalone version of Android Auto, utilizing your phone’s screen instead of requiring an Android Auto compatible head unit to be installed in your car.
Slowly rolling out over the next few days the latest version of Android Auto will be available in over 30 countries to users with an Android 5.0 or later phone. Functionally it will be fairly close to how Android Auto operates with a built-in head unit, with the most noticeable difference having to use a much smaller screen on your phone instead of the standard 6” or larger screen with an Android Auto compatible stereo.
Other missing features will be that you will not be able to use your steering wheel audio controls to operate Android Auto as well as for the time being not being able to use the “Ok Google” voice command (at launch you will have to tap the microphone icon on the screen to initiate voice control but this feature will be added in the upcoming weeks).
Look for our upcoming review comparing the Android Auto standalone app vs. using a built in head unit.