The problem is, if it's not on, then how would it know to connect? There's a "cart before the horse" issue there. Any system that requires wireless conection has to know when to connect, and the way to know can be any one or more of several different triggers. Proximity to a wireless location - whether it be a WIFI or Bluetooth device in proximity, or simply a specific location such as work, home, etc., , a specific time and/or day, receiving a signal on that wireless system indicating that a device wants to connect (which requires that the radio be on and listening), a NFC tag, other hardware trigger such as a docking station, etc. can all be triggers.
If you're looking for a system that can somehow know intuitively that you want to use your bluetooth speaker, but not have to keep the Bluetooth service running to be looking for it, then there must be SOMETHING that tells the device you want Bluetooth to turn on and connect to the awaiting device...there must be some other form of trigger in order to activate the radio and connect. Any form of trigger except perhaps a hardware one, will in fact use power. For instance, a NFC tag to turn on Bluetooth will require NFC to be running, and even though it's a very low power device it will still use battery power. Even a timer-based trigger or a proximity/geography-based trigger would require power (to run the background timer service or the geographical location device/service, such as GPS). On the other hand, a hardware trigger such as a USB port connection or a magnetic sensor would use virtually no power as they would be more like switches that are closed when the proper situation arises, such as plugging into the car USB port, or putting the phone onto your desktop dock that has strategically placed magnets (as was the Droid 2 and Droid RAZR MAXX on their custom Motorola Dock Stations).
I am trying to think outside the box here, but I see no other way to have a device intuitively turn on and connect to Bluetooth besides the ones mentioned. If I'm missing something, please feel free to add/embellish/correct/debunk.
