Stargate Atlantis, Season 5

Dr. McKay:
Controlled magnetic harmonic resonance.

Dr. Jackson:
What?

Dr. McKay:
Apparently Tesla was close to something like this before Edison trashed his lab.

Dr. Jackson:
What are you talking about?

Dr. McKay:
That wall was specially designed to destabilize when bombarded with a very specific harmonic resonance. That's what the tones were. And the strong magnetic property of the particles is what keeps the door from just crumbling into dust. It's a great way to hide a door, because you know, if you're looking for a door to open it's never going to be found. It's like a hologram, only better because it's solid mass until the tones are playing.

Dr. Jackson:
Right, so you could've just told me to walk through the door when you did it.

Dr. McKay:
I could have, yes.