Are there any apps for recording police interactions?

imagine an app that is sort of like a panic button. You get pulled over, you open the app and hit the button which then (depending on your preferences), starts recording/streaming video and audio, locks the phone, and maybe starts recording accelerometer/gps data, etc.

It would need to be thoroughly developed/tested before actually it could be ethically recommended.

What do you think? Good idea? Bad idea? unfeasible? Already existing?