The U.S. Air Force is experimenting with using robotic vehicles to help guard air bases. The air force has used some robotic vehicles for security for several years, but it is now equipping them with weapons and voice capability to allow for interrogation of intruders, and the use of lethal and non-lethal force if the intruders dont back off. Building these robotic vehicles is easier today because there is a lot of effective terrain avoidance software and hardware (sensors) available. You can see this by the fact that, for less than $200, you can buy a Roomba robotic vacuum cleaner. For about $200,000 you can modify an all-terrain vehicle to make its way around the perimeter of an airbase, through just about any kind of terrain, and transmit videocam views of what it around it, to a human controller many kilometers away. The controller can monitor several robotic sentinels at once, as the software will give an alert if a sentinel encounters a suspected intruder. There is motion detection software to handle that. The controller can then use a translation device to announce one of dozens of phrases (stop!, drop your weapon!) via a loudspeaker on the sentinel. The sentinel can also carry a remotely controlled weapon (rifle or machine-gun), or something like a pepper spray dispenser. The remotely controlled weapon system is currently used by American troops in Strykers or armored hummers. The air force is taking the lead in the use of robotic sentinels because it has airfields all over the world, often in out of the way, and unruly, places. Moreover, airfields tend to cover a lot of territory, and its expensive to send air force security personnel to these distant bases, and not always easy to get reliable locals to do the guard duty. So the robotic sentinels are an attractive alternative.