A watch implant is also something I’ve been mulling over for a bit now. This is one use case where there actually is a satisfactory power source available in the form of betavoltaic cells. Other types of nuclear batteries use heat (thermionic emissions) to generate power, which is inefficient and requires a very active and dangerous source like plutonium. Betavoltaic cells use tritium decay (like our old friend the xGLO) which is directly convert into energy in a process similar to solar panels.
The reasons we’re not using these for everything are:
- microamps of power
- currently very expensive
- currently very bulky (for an implant)
But for a watch implant, all of those limitations are negated. It has to be reasonably bulky for readability anyway, there is already a market for high cost-per-unit watches in place, and watches require very little power. You would only need a few μA to keep the time, and you could store any extra in a capacitor that would dump into the LED display when you infrequently wanted to view it (maybe with an arm shake).
Betavoltaic cells are currently available from some retailers like citylabs. They’re still pretty expensive (~$2500 IIRC?) and large (16mm x 16mm x 4mm). I’m just waiting for the technology to catch up and become cheaper/smaller. There’s not a large market push, so we’re might be waiting awhile. Luckily they are making some amazing progress on thin film semiconductors as a byproduct of electric car development, so we might see some accidental discoveries in the next few years that bring this forward leaps and bounds.