Q. Power and storage consumption

Ok, the other option is to simply do:

setWatch(function(e) {
  console.log(e.time-e.lastTime);
}, B7, {edge:"both", repeat:true});

Hopefully that'll dump out a bunch of times (assuming the signal is getting through to the pin). If you take the shortest time you see appearing relatively often and then do 1/time you should get the baud rate of the signal.