You need a heat difference, not just heat, to generate electricity. Now my sibling comment links to a paper where they say they can find heat differences in th

You need a heat difference, not just heat, to generate electricity. Now my sibling comment links to a paper where they say they can find heat differences in the body that are sufficient for their needs, so this is still a possibility! But it does mean you need to be somewhere with a heat gradient: the paper mentions just under the skin.