WiFi equipment can see your heart beating, but don't worry, it cannot possibly have any harmful effects on human physiology.
A sonogram can see your heart beating too, but no one thinks sonograms are dangerous(because they are not).
Unsolicited remote sonograms are stopped by walls, floors, ceilings and doors, unlike wireless radio networks.
A concrete wall stops wifi pretty well.
How thick a concrete wall is needed to stop wifi? Or does the concrete wall contain fine wire mesh?