renauly radio on/off?

does any1 know why my 2002 laguna radio wont turn its self on or off automaticaly?? i have to turn it on when i start the car and turn it off when am gettin out of the car, and a few times i have put the radio on mute to take a call and forgot about it, not goood if the battery died when i was out... if any1 could help please email me at djcallo07@hotmail.co.uk thanks