For spies: with the iPhone settings you can discreetly shoot video: it will appear to others that your phone is on lock or turned off.
How to do it:
1. open "Settings" and select the "Universal access" section.
2. Then click on "Display Adaptation." On some models it may be called "Display and Text Size".
3. Turn on "White Point Reduction", reduce to a minimum. Do the same in "Light Filters" with the intensity of bright colors.
4. Turn on the camera, open the control panel and reduce the brightness of the screen to a minimum.