Background task indicator

Is it possible to have some indication that a background task is running? I’m writing an app which connects to a device receiving a stream of information for about an hour at a time. I’d like the user to be able to continue using their mobile but have a discrete indication that data is still being received. I see from another thread that floating apps or screen widgets aren’t possible without native code. I’m thinking of subtly ‘breathing’ the screen brightness. Any suggestions gratefully received.