Tone

The people I know with answers won't give them when asked.  So I have a few Questions.

   There are several ways to achieve X-ray vision.  It doesn't even take glasses from the back of a comic book.  If you want to know what items may be somewhere you can't physically go...  there's always tone.

   Pretty much every item in a home or business (excluding jello) will resonate in response to a loud enough sound.  It's just like 2 tuning forks side-by-side ringing in sympathetic vibration.

   There are a few limits if you want to use sound that way.

   Most home owners wouldn't enjoy giant speakers placed outside their residence to rattle everything in it.  That would also ruin the element of surprise.

   You'll have to be sneaky about it.

   Find a way to cause items inside the home to resonate that in turn would cause other items to resonate.  Ideally you'd use something completely undetectable to start with.

   You might be wondering what that might be.

   RF (radio frequencies) of course.

   Something along those lines will cause metal objects to resonate (also electronics but I didn't tell you that).  That can then trigger sympathetic vibration of other objects.

   When the vibration (also known as frequency) becomes loud enough it can be picked up outside the home.  When the frequency is low or high enough it can escape notice by the residents.

   Now all you need is a database of sounds objects make.

   It's expensive finding someone with the skills to do that manually.