Research the Houdini Splicers until you get the Natural Camouflage Tonic. If you have this equipped, you will become invisible if you remain still. This will protect you from Splicers, Big Daddies, and Bots if you set off an alarm. If you move again you will become visible. You cannot become invisible if an enemy sees you. If you are invisible and an enemy besides a Bot touches you, they will see you. The cameras and turrets also cannot see you if you are invisible.