MorganS:
Where is this device going to be sitting when it's pushing down on the door handle? Is it bolted to the door?If it's a floor-standing robot, does the door open towards the robot? (difficult to back out of the way while holding the door) or does it open away from the robot? (now your robot is in the way of you going through the door and it can't reach the door to close it behind you.)
It will be bolted to the door