There are limits to the DIY movement, you know? The Motherboard channel of Vice has the story of Tim Cannon of Grindhouse Wetware, who inserted what appears to be a larger-than-necessary sensor under his skin to monitor his temperature. It happened at a body modification conference in Germany.
Oh — and there are status lights that shine through his skin and light up his tattoo. But hey: it uses Bluetooth to transfer data.
And there, of course, a video. Though not, thankfully, of the actual implantation (which was not done by a doctor, by the way).[youtube https://www.youtube.com/watch?v=clIiP1H3Opw#t=310]
Still interested? It’s open source. There are code and schematics available.