Factual error: There is a shot of the Imperial Valley at night with the edges of the Los Angeles destroyer spinning over the mountains. The center of the destroyer is hovering over downtown LA. Imperial Valley is over 200 miles away from downtown LA, and the destroyer is no more than 20 miles in diameter. There would be no way the edges of the destroyer would extend far enough to be seen from Imperial Valley as shown unless it was over 100 miles in radius. The ship does not even hover over Steven Hiller's house which is in LA, it can nearly be seen whole from there. The destroyer would be obscured by the mountains and from 200 miles it would appear much smaller.
Factual error: David is in New York playing chess and then goes to the station riding his bike through the office. When he goes past the vending machines, the water machine is Arrowhead branded, which is a California / west coast water brand - not on the east coast. (00:07:00)
Continuity mistake: The missile used in the mother ship had a 30 second count down. From time of launch to explosion was one minute thirty-six seconds.
Factual error: Aliens are using TV satellites for their secret attack signal, making the TV picture quality poor. David shows the president how they do it by bypassing the curvature of the earth. However TV satellites don't work that way. They are "hanging" pretty much above their broadcasting area totally reflecting and spreading the signal back straight downward to earth. Turning the parabolic mirrors of the satellites to a different elevation would result in no TV signal on earth, not just a degraded one.
Suggested correction: Satellites do both. They both send the signals back down to earth but they also send signals to each other in order for the signal to cross the globe. And in those signals the aliens have hidden their own signal, and that distorts all satellite signals, causing TV's to receive a distorted signal.
Very few satellites directly talk to other satellites. Geosynchronous communication satellites don't. The antennas used for transmitting the TV signal are directional, but while directional antennas send most of their energy in one (or a few) direction, they still leak at least some energy to all directions, so it could still theoretically be used as described. The real mistake though is the aliens have advanced technology, so could easily have deployed a couple satellites of their own to perform this function, so why the need to use ones from Earth? Worst case just send a couple small ships up to act as relays.
It probably saves them time to use the satellites already in orbit. They are on a tight schedule and don't want to waste time and resources deploying their own satellites. Plus it's a small possibility for them that humans can take out their satellites, so hiding it in their own seems perfect.
They could be using the human satellites to disrupt communications or make communicating across the globe difficult to hinder any possible pre-emptive strike by Earth's armies acting in unison while the harvesters position themselves for the first wave of attack.
Audio problem: The same female scream can be heard three times during the first attack by the aliens. It is first heard in the scene when Jeff Goldblum is riding his bike to his father's house. The second time it is heard right as Jeff gets to his father's door. The third time is in Los Angeles when the people are running away. It's a very distinct scream.
Other mistake: When the US Military is deploying a nuclear bomb against the alien attacker over Houston, you see them fire the nuke and then the B-2 breaks left, but on the screen you can see the B-2 breaking right.
Revealing mistake: When the Welcome Wagon is being shot down you can see an explosion starting inside the last helicopter before it is even being hit.
Continuity mistake: Jasmine's friend at the strip club shows off a sign she made. It changes design and grows creases. This is more evident in the special edition, as the scene is longer.
Continuity mistake: When the alien spaceships open the main gun above the White House we can just see the green light coming on at two people on the ground. When the camera cuts to the view of the spaceship the gun housing is almost completely open.
Continuity mistake: Near the end of the film as the shields come down, the jets start firing missiles at the ship. There is a shot of Randy Quaid's son walking through the control room at Area 51. Notice in the background, the lights are blinking on and off. The alien ship hasn't fired it's main weapon yet. Once it does they show the lights flickering off and on in the control room. These scenes are several minutes apart.
Other mistake: When David asks Major Mitchell if he can shoot the soda can, Major Mitchell has to ask a nearby sergeant for his sidearm, despite already having one on him when he shot the alien earlier.
Suggested correction: He probably shot his own gun empty or nearly empty, so he removed the magazine. They fired at least 10 shots at the alien, and he planted another 3 in it up close.
Continuity mistake: As Smith leaves Jasmin to go to El Tore his uniform jacket's epaulettes are untucked then tucked and finally untucked again.
