This is about producing tiny amounts of electricity by radioactive decay from tritium. Products like that have been around for a while and they have some niche applications, but they're quite expensive and inefficient. They make a comparison with tritium exit signs but those by now are a pretty bad idea, compared to LED's and conventional batteries. The exit signs create a nontrivial disposal problem. They do still exist.

They say gadget has 20 to 40 curies of tritium so by my math that's around 5 milliwatts of thermal power (idk their electric conversion efficiency). About what you get from (corrected) under 0.5 square centimeters of solar panel averaged over 24h, plus some battery or capacitor storage. Doesn't seem that competitive.

The exit signs create a nontrivial disposal problem.

Do they? I thought the half-life of tritium was pretty short.

12 years.