Instead of a stand-alone piece of e-waste, how about this: a device with the same format (a ring and an button) but the only thing it does is trigger the pebble watch to start recording a message. This way the microphone isn't needed, just the radio (and much weaker radio at that), and the battery will last exponentially longer. Then just expose the charging terminals so that we can at least hack the device with cust…
The biggest downside is I don't think you can directly connect to the pebble for that it'll have to go through the phone. One advantage of the index if it doesn't rely on your phone to be available right then