The robot is attached to a spring. Passers-by can make it bounce back and forth by pulling a string.
ALL YOUR SURVEILLANCE CAMERA ARE BELONG TO US
Step 1: Go to your local hardware store
Step 2: The things you will need
2) A spring-like device such as this "Presto Whip" stirrer.
3) Bendable pipe (can be found in the plumbing section)
4) A threatening-looking robot (the more guns the better)
5) Some string and a "pull" sign.