"Voyeur Right Angle Spy Lens" £39.00
Point your camera one way and shoot the other with this right angle lens attachment.
This lens will allow you to film directly to the right or left of where your camera appears to be pointing.

I once saw a reproduction of an ad from around 1900 for a camera disguised as a small pistol.

It seems the idea was to let you take unobtrusive snaps of the sort of people that didn't mind if you pointed a gun at them.

I don't believe history records that anybody bought one.