Is it technically difficult to detect abnormal microwave energy in this kind of situation? I know you can get a microwave oven leak detector for about thirty dollars.
Let me tell you about the viennese hotdog stand owner who had three microwaves running at all time, to heat food quickly. Open. Behind his back.
There was a glass in between the customers and him, shielded, but the pressure of the microwaves (heat, i guess?) could be felt through the opening, where he hands out the food.
Of course it killed him eventually.