Did you know about this rock from Russia? It's supposed to neutralize wireless signals. I perceive a difference when I put it on my wifi-router, which I rarely use due to a kind of buzz I perceive in my head. But when I put a couple of these rocks on top, that buzz goes away. There's fake shungite for sale, but there's a flashlight conductivity test you can do to make sure it's real, and this passes the test:
It's also good to put some in your pet's water bowl, but you have to really wash it first to get all the black powder off it. I also put a stone in my water bottle.