Yes the enemies hear if you fire a bullet near them and come looking for you. eg near the beginning that second robot heard the gunfire and opens the door coming after me (I knew he was coming from there so waited.) Instead if you get closer to one and knife it instead it doesnt alert anyone nearby.
I am kinda done so wont add a hazard like you said, but if you watched the video there are things like rooms you can enter but cant exit until you find a key. And enemies that wait in cubbyholes until you walk by. Etc