Underground radiation exposure

So, we had this guy drop by recently—someone who claims to measure underground radiation levels in your house. He was waving around some little antenna device and telling us that the radiation hits hardest right around our pillows in the bedroom. His big "expert" recommendation? We should probably change how we sleep.
He also went on about how long-term exposure to this stuff could lead to epilepsy or heart attacks, among other things.
The guy kept citing these studies done over in France at some institute, though he couldn't quite remember the actual name.
After dragging us through a three-hour presentation, he basically tried to corner us into buying this special radiation-shielding mattress. Apparently, it improves your overall health and all that nonsense, and he offered it at a "bargain" price of $2667.
Long story short: is this just a massive scam, or is there actually something here we all need to be worried about?

Look, don't fall for that nonsense. There hasn't been a single legitimate study to back any of it up. Endymion has already posted extensively on this topic, and honestly, there's no point in wasting more ink on it. Bottom line: it's a massive hoax.