When you record your face for the unlock, strike a pose that is not your default expression. Put your hand on your face with the sherlockian "hmmm" expression.

When you record your face for the unlock, strike a pose that is not your default expression. Put your hand on your face with the sherlockian "hmmm" expression. Guards/police won't know, they'll just hold the phone up to your face and try to unlock it.