Robots are going to do many things for us in the future, including serving as a mall cop. Take Knightscope K5 and K3 for instance. They are designed to gather data and keep and eye on things. These robots use sensors, lasers, and smart software to autonomously roam a geo-fenced area.
The K5 is capable of navigating around objects in indoor and outdoor environments. This particular model weighs 300 lbs, measuring 5 feet tall / 3 feet wide. The K3 is more compact, measuring 4 feet high and 2 feet wide. More info is available here.