The normal evolution of energy-producing devices typically involves many iterations of technology development and scaling up, until the device produces enough power to be both useful and economical. Wind turbines are a good example of this path. But an article in MIT's Technology Review describes an interesting technology that has followed a very different path, effectively waiting until the power needs of potential applications become small enough to match the modest output of the energy source. It won't be running your car--or even your cell phone--anytime soon, but it could be the key to unlocking the vision of tiny, ubiquitous radio-frequency sensors for civilian and military applications.
Beta radiation, in which radioactive substances emit electrons as they decay, was discovered over a century ago, but it has taken this long to find an application that matches the relatively low electric currents that can be produced by harnessing this kind of radiation. These "betavoltaics" are entirely different from the nuclear batteries that have been used on unmanned spacecraft for decades. Those worked by turning the heat produced by the decay of a radioactive isotope, usually Thorium, and turning it into electricity.
While betavoltaics may end up being useful only for battlefield sensor networks and their non-military analogs, you never know. Perhaps some other nifty new technology will come along that will only be possible with this kind of power source, and that we won't be able to live without. But just as millions of people today believe that cell phones and power lines cause cancer, putting anything powered by beta-decay into our homes could be a pretty tough sell.