IIRC this is about people getting sick within certain rooms and buildings. You wouldn't need to penetrate far through walls if you could plant a device somewhere within the room itself.

Also people think "microwaves" mean heating waves used in ovens. That's a wrong impression, microwave ovens use very specific frequencies that resonate with water and fat molecules in food. But the spectrum is much wider than that, for example WiFi signals are also in the microwave range.