Just a friendly reminder to flight deck crews, make sure to close that cockpit door when shutting down the plane or leaving it unattended. I just had a gate agent go into the cockpit, after I had shut it down, and turn on the ground power button shortly after I left. Luckily I went back for something and saw the airplane powered up. Apparently the gate agent thought it needed to be on in order to get lights in the cabin, which is not necessary on the 175. I'm sure the door would not have stopped him but it might have discouraged him from ever going in there to begin with. Had I not discovered it I'm sure I would have gotten blamed for it in the morning.