android - Automatically connect to paired bluetooth device when in range

Question

Goal:

I'm trying to get my android service to auto-connect to an already paired bluetooth device when its in range.

Example:

I have my iphone paired to my car. When I sit down in my car music starts automatically playing. I don't need to connect it again. I don't need to start a song. It just launches itunes and starts playing music. I want this kind of connectivity in my Android application.

One obvious solution is to have a thread running in a background services that tries to connect every X seconds. This however is not optimal due to the toll on battery life.

I tried setting up broadcast receivers to get triggered on ACTION_ACL_CONNECTED but this seems to only get called after I connect to the device.

Is there no way my app can get a notification when the phone walks into range of the device?

I've spent the better part of the last two days trying to get this to work with no luck. There are a billion tutorials on how to connect to a bt device but none to auto connect when in range. Starting to question if this even possible.. I'll be blown away if its not :(

related questions:

Find already paired bluetooth devices automatically, when they are in range

Answer 1

As far as I know there is no way to automatically connect to a generic Bluetooth device as soon as it's in range. Your best bet is to have an inquiry loop, periodically querying available devices and connecting to ones you are bonded with (although, as you said, this is fairly battery intensive).

However, if your device (both the phone and the peripheral) support Bluetooth 4.0 (LE) as well as GATT, you can use connectGatt method that will automatically connect as soon as the device becomes available (again, not too sure about battery implications although limited testing I have done thus far shows that it is not significant).

I'm not entirely certain what the behaviour of connectGatt is when device is non-GATT but it may be worth investigating - my guess would be that you'd receive a callback with status GATT_FAILURE when device becomes in range but doesn't support GATT (this would at least give you an indication of when to connect).

If you find a solution or investigate the behaviour of this method on non-LE / non-GATT devices please do update your question as I'd be quite curious to find out more about it.