knocking
lean against the wall and knock on the wall. near by guards will check it out with out setting into alert or caution. run around said wall while they move around. to check where you were. mags
if you toss a magazine by a guard he'll check it out and make it easy to sneak up pull him in a CQC head lock and knock him out or just run by. for no kills
be aware that the smaller robotic gundom-ish troopers in the second act are piloted by a living person so killing them counts but u will need to dispose of them. my personal weapon of choice is using the shot gun with v-ring. there is an auto shot gun that a clip makes short work of them and deactivates them in with out killing them and it has good range. the last level no alerts
you start on caution and have jump happy frogs all around you. run to the right and strait ahead you'll find a latter. climb it and you should be relatively safe just don't be an idiot and make noise or be in the open. trank every one you see head shots work best but the mk.22 is hard to use. just get good with it and use the iron sights its more accurate. remember when moving down the hall ways the frogs will drop right in front of you so move cautiously and since they drop in pairs chances are you cant take them both out before they spot you so role to cover and take them out one at a time or let them pass. its better if no one is awake to stumble on you but if they die they are quickly replaced