Buzzing warning to turn off your BOSE system

[PlyBoyDoct@aol.com]

I have the BOSE  system and I like it very much.

I forget to turn it off when I get out of the car sometimes.  I never run out 
of battery yet, but I dont want to chance it.  I recently sat in a 93 100 
with the bose system and when I turn on the stereo and had the door open 
there was a buzzing sound and upon turning off the bose system it turn off.  
I was like "NEAT!"  How do I do this for my car?  Does my car already have 
this broken option or I need to fit a few relay in my car?  Any ideas?  

Jason C
89 200t10v
Redmond WA