Bluetooth scanning works without bluetooth turned on android

Question

I am creating an app with Bluetooth Low energy. There is one interesting thing I found out. I know that for API level 23 or higher you need to give permissions for location in addition to bluetooth for the scanning to work. But I didn't know you could scan for ble devices even when the bluetooth is turned off from settings. I had bluetooth turned off(but location was still on) but I could still see ble devices from scan result.

Is this a bug in android, where android internally uses bluetooth without the user being aware of it ? or is this documented somewhere which I couldn't find.

Answer 1

No. This is completely normal. In Android M they adjusted the permissions / added the feature to use Bluetooth for location. For this to work your phone only needs to listen for other BT devices. It doesn't need to broadcast itself. This is a much smaller privacy concern since you aren't leaking your own presence to other BT devices.

You can read more about it here on Android Police

I'll admit that the user-facing description is weird: "...scan for bluetooth devices, even when Bluetooth is off." Obviously the BT antenna isn't really off. It has to be on to listen for other BT devices. But at a software level, the BT stack is not broadcasting its own address.

It's not clear if or how much this saves battery life since the BT antenna is still on.