'Auto car bluetooth' automatically turns on the bluetooth when you get in the car so that it connects to the speakerphone and turns it off when you go down to avoid unnecessary battery wastage.

Basically the app uses Google's activity_recognition service.
In the app you can set three variables:
_ Detection interval
_ Confidence value
_ BT OFF timer


Each "Detection interval" seconds the app reads the status of the activity_recognition service of Google.
If that service returns at least for "Confidence value"% of times the status "In_vehicle" the app turns on Bluetooth.
However when the "In_vehicle" status is not recognized for "Timer BT OFF" seconds the Bluetooth is turned off.