Frosted Film, Spray Frost, is about it if you don't want a curtain or blind.

Like the stuff people use at Christmas time? Does it look good?

Google 'Decorative Window Film'.

That door is pretty easy to break into. Consider buying a new door - with a tiny window in the center. Use the front door somewhere else in your home.

Clear Contact paper can be used as a window film. Cut each piece slightly larger than the window pane. Spray a little soapy water on the window first, position the film, and use a piece of plastic, like an old gift card, as a squeegee to push all the air bubbles from under it. Dry the edges with a soft cloth and trim the excess with a razor.

"Like the stuff people use at Christmas time?"

No they make a spray window frost that is NOT easily removable, xmas stuff wipes right off.

"Does it look good?"

Define "looks good", lol. In my opinion, mediocre at best as it is not permanent to the glass.