Strange question about home security...

You could use flour, provided the room is dark.

 

Or you could use a tiny camera the intruder wouldn't see.

 

There was a trick in a Bond movie I really liked: putting a hair across the juncture between a door/window and its frame to see whether it had been opened. I think he just slicked his fingers a bit and laid the hair across. If the door or window is opened, it would just fall off, and it's incredibly inconspicuous. Don't know how practical it would be, though.

Also, if you use something like household laundry detergent, it will fluoresce under a blacklight. Maybe something to consider.

 

If you don't mind my asking, what's your story about?

 

I'm talking about the powder, specifically. It might be problematic to get a layer that is simultaneously uniform and inconspicuous, though.

 

Story purposes. Uh-huh.

 

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Any sort of powder would be pretty obvious but a common trick is too put a piece of paper in the crack of the door so that it will fall out if the door is opened. Even if the intruder see the paper and recognizes what it is for he would have no way of knowing exactly where it was to put it back.

 

This was Dr. No. Another thing he did in that scene was put powder on his suitcase to see if anyone tried to open it after he left.

Another suitcase trick was in Goldfinger. If the catches weren't turned a certain way, a canister of tear gas would explode when someone tried to open it.