Fog systems are usually combined with a remotely monitored intruder alarm. When detection devices trigger, the fog device rapidly blows a cloud of dense, white smoke into the area around it. The fog isn’t harmful and the systems can be designed so they’re effective in small spaces like a shop, or a large open plan warehouse.
The idea of these systems is to deter burglars, and then make it very difficult for those that persist to locate goods within the protected area