There are saliva tests, which is probably as non-invasive as it gets. They're currently not quite as accurate (about 95%) as nasal swab tests (99%, if applied c

There are saliva tests, which is probably as non-invasive as it gets. They're currently not quite as accurate (about 95%) as nasal swab tests (99%, if applied correctly) but still good enough to catch most infections. The biggest problem with these tests probably is getting a proper sample. Still, that's at least by orders of magnitude better than simply doing nothing. Besides, an accuracy >= 95% with results in less than 15 minutes isn't that bad at all already.