I am working on a project that would interpret a signal from an Arduino and turn on music/adjust the volume in a bluetooth earpiece when a certain threshold is reached. This needs to be wireless (i.e. the Arduino is in a fanny pack around the waist or something like that). Is this feasible/possible? What sort of hardware would I need?
Probably not. The source of the music is unclear. If you want Arduino to control the device, all your problems would be at the bluetooth earpiece end.
This kind of thing does already exist, so it must be possible. Think about how the existing devices work and think about how the arduino can replace or insert into the chain.