It's impossible to write about crime-fighting robots and not mention RoboCop, so let's just get it out the way right now. Although, these crime-fighting bots from startup Knightscope are a long way from the menacing machines made by megacorporation OmniCorp in Paul Verhoeven's movie.
In fact they don't look aggressive at all, more like they've stepped off the set of a 1970s sci-fi series. Still, the K-5 security robots are slightly imposing standing at 5ft tall and weighing 300 pounds—and they're fully autonomous. They are, however, unarmed so won't be throwing around any lines like "Dead or alive, you're coming with me."
Instead they're meant to act as a kind of deterrent along with being informants. They won't give chase if they see a crime being committed by they will record it and send it back to a command center where a human will be watching.
If they catch, say, a burglar in the act by noticing the sound of broken glass for instance, they'll be able to get a picture of any vehicle the criminal(s) might be using, along with geo-tagging the place and time of the crime.
They use a similar tech to Google's self-driving cars to move around without bumping into anyone, something known as LIDAR (Light Detection and Ranging) which creates a 3D map for them to navigate with using pulsed lasers.
If they are attacked the bots will let out a loud chirping which will notify the command center and the sound will get louder and louder if the threat continues. The idea being presumably that no would-be crim is going to want that kind of attention.
As for where they'll be patrolling, at the moment they're being used on corporate campuses and some Silicon Valley malls. Those types of places, along with college campuses and data centers is where they'll be deployed and where Knighscope says the demand is, aiding security guards and police rather than replacing them.
As long as they don't start issuing commands like "You have 20 seconds to comply" then the public will probably see them as a welcome addition to fighting crime.