[rowanajmarshall]

Going by a random Reddit thread [1], it takes less than 5 calories to charge an iPhone. I think that kind of device is already on the market though.

You're not gonna power a heater or aircon through body movement, but devices should be fine.

1. https://www.reddit.com/r/theydidthemath/comments/693daq/comm...

[Dylan16807]

It's just a unit conversion, you don't need to cite reddit.

A Calorie is slightly more than a watt hour.