Corrected entry: The parents set up fireworks as a noise distraction but this has to be triggered remotely, away from the house. Surely there are other ways that noise traps can be set which can be triggered easily from the house. Or from a remote control. They have plenty of electricity.
Corrected entry: How did the Death Angel reach the basement while it got flooded? It seems to have magically appeared, and never took the staircase.
Corrected entry: Though the film takes place over many months, the crops in the field near the house never seem to change appearance.
Corrected entry: If the aliens are sensitive to sound, and a simple high pitch sound can distract and hurt their hearing, the army could have figured this out long ago and defeated them with ease.
Corrected entry: Although it has been 450 days, the wife has a calendar to track her pregnancy. Who printed that calendar if it has been more than a year since the demise of civilization?
Corrected entry: When the power to the Abbotts' home goes out, the hundreds of colored lights and all of the cameras and monitors in the basement continue to work normally. This would have required either a really large generator (which would have made noise) or an incredible number of backup batteries, which weren't available to them.