Take photo when unlocking

Hi all,

as I am not sure whether some people (that have my unlock key) are sneaking on my iPhone, when I am not arround, I am searching for an App, that takes a photo, as soon as it is unlocked. No matter, if it is the right or wrong code.

Is there anything on the market? The App Big Brother is completely senseless.

Or is there a setting in iOS which I could activate?

Cheers and thank you,

N.