Factual error: When they launch the F-16's to intercept the Soviet "Backfire" Bomber, the picture shown is of two F-15's. In addition, no F-16's were stationed in Alaska to handle air defense duties, this was handled exclusively by F-15A/C's.
Continuity mistake: During David Lightman's escape from the infirmary, notice the hands of the guard officer - he's wearing his gloves, and the next instant they have disappeared, and reappear in the next scene.
Revealing mistake: In the scene where David starts the game with Joshua, it asks him what side he wants to be (1 for the U.S. and 2 for USSR). Look carefully at the closeup of the computer screen - his choice, 2, appears long before David actually presses the key.
Audio problem: When Jennifer gives David a ride home near the beginning of the movie, you hear David's dog barking. In the next shot, we see the dog is running down the front path and it barks a couple more times. Look closely at its mouth, it's not barking.
Continuity mistake: Towards the end when the NORAD door is closing, they keep showing it opened further from shot to shot in order to delay how quickly the door actually is closing vs. how slow it really would have had to move in order to allow David and Dr. Falken to actually have still made it in.
Continuity mistake: The tour group comes in and they trick the black lady into pressing the red "launch" button that displays the welcome on the screen. Just before she presses it she has a 35 mm camera hanging around her neck, but in the next shot of the group standing in front of the panel her camera is gone.
Factual error: During the part where they're in NORAD and watching all of the Soviet "nukes" hit various bases in the US, a base in northern Maine is listed as, "Loring AFB 43 Bomb Wing." This was a real air force base, but it was the 42nd Bomb Wing that flew B-52s out of Loring. The 43rd Bomb Wing did exist, too, but it was based at Andersen Air Force Base, Guam, in the North Pacific.
Plot hole: McKittrick says the computer will not accept the launch codes unless they are at DEFCON 1. At the end of the climax the computer is trying to guess the code while they are at DEFCON 1. So why couldn't they just go back to a different DEFCON before the correct code was guessed?
Other mistake: When Jennifer meets David in Oregon she says she drove 3 hours to get there. In the next scene they are getting off a bus to catch the ferry. What happened to her car?
Continuity mistake: In the very beginning, when the Air Force brass land at SAC in the helicopter, they get into a 2 door Jeep Cherokee. After they enter the tunnel and stop to get out, they exit a 2 door Jeep Cherokee Chief - the wide wheel well model, not the standard one they first got into.
Other mistake: When David first logs into the system after finding the right password, it shows a phone # beginning with the prefix 936. The only problem was that earlier when his computer was dialing numbers, he had not gotten to 936 yet. That was the 4th prefix and he only got through the first 3. There is no way he could have dialed that number with his computer program.
Continuity mistake: When David and Jennifer leave Falken's house, it is fully dark out. When the helicopter is shown flying around to pick them up, the sky changes from fully dark to some twilight in the sky, depending on the angle shown.
Audio problem: When Jennifer gives David a ride home near the beginning of the film, as David gets on her bike, she looks round and tells him to "Hop on" without moving her lips.
Continuity mistake: When Matthew Broderick is first at his computer the screen is large and has an external modem on top. Later there is a close up shot of the keyboard and the monitor. At this point the monitor is completely different and much smaller. Then shortly afterwards you can see the larger monitor again with the modem on top (behind Ally Sheedy) while it war dials numbers. Shortly after that, the monitor changes again. You can also see the changes with the color and the "side handles" used for carrying. I counted three different monitors being used.