When the old lady's cat jumped out and scared her before David came on the screen. This was a suspenseful moment because as a viewer, you know what David is capable of and when he hears that the woman has been talking about him, he immediately knows he needs to take action. At the point when the cat jumps out at the woman, the audience are on the edge of their seat because they know that at any point they are going to see David come out of nowhere and do something to her. The cat was just used as a false plateau.
The shower scene with Michael had suspense in it because when in the scene before, he is apprehensive about David and so is very careful of what he says and does around him. When he comes out of the shower, there is no music, which gives the assumption that at any moment something is going to happen and when Michael walks to the door and opens, the suspense is being built and at that point you see that David is standing right there which makes the audience have a visceral effect of screaming or jumping out of their seat.
In the second to last scene, starting from when Michael goes into the basement to try and find something out about David, a lot of suspense is created. When Michael's girlfriend, Kelly, tries to call him because she sees David, and his phone drops on the floor, immediately suspense is being created because as the audience you don't know whether he is going to make it out in time or if David is going to catch him. Also, in this scene, when Michael runs to the stairs of the basement trying to get out and finds out the door is locked, the suspense is again built as the audience know David can hear his screaming for Kelly, so they know that something bad is about to happen. - (Bomb Theory)