Project IGI had local and global alarm systems. E.g. with two bases on the map, alerting the first base would spawn a massive number of soldiers (a regenerating

Project IGI had local and global alarm systems. E.g. with two bases on the map, alerting the first base would spawn a massive number of soldiers (a regenerating pool of 4-~15 soldiers) and some other stuff, e.g. tanks, while increasing patrols in or around the second base or turn NPCs from an idle pose to a searching pose.