I think if I were to make a couple mods for wearability, they'd be a slightly smaller size, a square of bare tinned space so the solder mask doesn't have to be sanded off for the clip, and a coin cell holder on the back, as the battery pack is a problem when you're wearing it. I'm just going to glue a coin cell holder to the back of this one and wire it in. But the joy of an open source design is, I need some more practice with Eagle. I can fire up the open files that are provided, and make those changes.
How long will the batteries last? (2xAA) +/- ?