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:

Natural mineral from Karelia, Russia

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.