The author wrote a nice set of series on how to talk to other devices over bluetooth on android. Well for programming that is.
http://www.lucadentella.it/en/2014/03/11/android-e-bluetooth-1/
http://www.lucadentella.it/en/2014/03/18/android-e-bluetooth-2/
http://www.lucadentella.it/en/2014/04/28/android-e-bluetooth-3/
http://www.lucadentella.it/en/2014/05/02/android-e-bluetooth-4/
http://www.lucadentella.it/en/2014/05/04/android-e-bluetooth-5/