You could theoretically look through all the walls with an old dental X-Ray unit. I remember reading an article on here about someone who reverse-engineered an

You could theoretically look through all the walls with an old dental X-Ray unit. I remember reading an article on here about someone who reverse-engineered an X-Ray-sensitive camera module and used an old dental emitter as the source. All the radiation shielding would obviously be get important. :D