This attachment fits onto most lenses via adaptors. Looking into the side opening, you can see a precision mirror that reflects light into the optics. The swivel barrel lets you take discreet shots in any direction without having to point the lens at the subject.
Photojojo's Web site lists the price of the Super-Secret Spy Lens from $50 (£35) to $85 (£60), depending on which combination of adaptors you require.
Photo credit: Photojojo