Yes. I was just thinking that because headphoned is already listening to the headphone state it could probably also be used (after some modifications) also to see if some signals are emitted from headphones.

If I am correct the phone app is listening (or the incoming/outgoing call awakes something that is listening) to the signals from the AV connector (it has to be, otherwise the call ending button would not work). I think it should be possible to make also other apps to sense the button presses. I thought that headphoned would have been a logical place to start the investigations/additions.

I asked thp, the author of the headphoned, in other thread if I have understood his app correctly.