One of the special characters, a female spy, can distract multiple guards by dancing. Some abilities are the same, or have the same effect across commandos. For example, a couple of the commandos can knock out an enemy with a punch, and the spy can have the same effect with a chloroform-laden cloth. Forming your opposition are the guards. There are a couple of different types of guards, the only major difference between them being that the Gestapo cannot be fooled by your spy.
Some guards are stationary, surveying an area from a fixed position, while some run routine patrols.
You can shift-click on a guard to see his field of vision, represented by a green cone emanating from the guard. At long range if your commando is prone they still be might not be seen, whereas at close range they don't miss a thing, including bloodstains from a previously dispatched guard. Although the guards are armed differently and have different accuracy with their weapons, it doesn't make much difference because once the alarm is sounded, the mission is pretty much over. When the alarm sounds, guards rush out of every building, meaning a quick death for the commando who got spotted, and losing one commando means failure. About the only time an alarm doesn't mean instant game over is when you are making your getaway at the end of a level.