When Nicole shuts the door to her part of the apartment to keep Michael out, you can hear her locking it. But throughout the film there is no keyhole or lock visible on either side of her door.
Cooper complains that he can't sleep because he can hear the ocean. However, Nice, on the French Riviera, only borders the Mediterranean, which is a sea, not an ocean. The nearest ocean, being the Atlantic, is at least 300 miles away.