How to safely kill houseplant fungus gnats?

Thank you for your prompt response. I am planning to try all of the recommendations that I receive on this forum. I'm guessing I might be able to find this powder you suggested at a farm supply store. We don't have nurseries nearby

Thank you for your prompt response, Wma7908878. I am going to try this. We sprinkle cinnamon on our coffee grounds prior to brewing and several foods for its health benefits. Will be interesting to see if it has the opposite effect on insects

Thank you for your prompt response, Fiddledd224. Tried your suggestion...unintentionally, on two separate occasions while we were out-of-town for over a week each time this past the summer. Plants were very thirsty to the point of wilting leaves. Seems like it didn't kill the gnats, since the eggs are buried in the soil. Soon after watering the plants, the bugs emerged. I also read online that this particular brand of potting soil (new bags) has been known to harbor the fungus gnats...ongoing with each new year's supply. I thought I was being ridiculous in suspecting the soil was contaminated last year when I first encountered the problem. I wasn't

I have used Windex for over a decade to kill all indoor pests, as well as hornets and wasps and have even sprayed it on the leaves and soil prior to watering. It successfully and safely eliminates topical and flying insects, but does not touch the larvae/eggs in the soil

That would require unpotting, completely washing ALL dirt off of the roots, microwaving, then repotting. The gnat larvae are already in the soil. And how would they get in your food if they are dead???