Sometimes I can touch people and they won't be alerted but most of the time they turn around when I am still 5-6 feet away.
Also on most levels the music cuts out and makes it impossible to finish a level with SA ratings. On Tubeway Torpedo this happens a lot. The music cuts out and audio gets messed up before getting into the first basement level and then the pager/phone trick does not work. The general never hears the beeping so you have to shoot him through the glass.