Factual error: Area 51 is located in southern Nevada (the movie acknowledges this), but the security gate that Steve Hiller enters through is shown to be in the Bonneville Salt Flats, which are located hundreds of miles away in northwestern Utah.
Continuity mistake: When David shows up at his father's house, Julius opens the door pointing a gun at his son. David grabs hold of the barrel and in the shots facing Julius, David lets go, but in the shots facing David the barrel is still pointing up which David is still holding firmly.
Continuity mistake: At the decimated MCAS El Toro, when the First Lady asks Jasmine what she does for a living, the First Lady holds the bowl out with her left hand in the shot facing Jasmine, but in her right hand in the shots facing facing her. The direction of the bowl's handle also changes.
Continuity mistake: As we hear the biplane's engine closing in on Miguel Casse, as he rides the motorbike down the road, in the overhead descending shot his shadow is to his right, but next shot as his crop-dusting father passes over him the shadow is to his left.
Continuity mistake: In the interior shot, when Jasmine tries to explain why she doesn't want Steven to leave she pulls open the white curtains, to view the alien ship through the window (the window closest to the door), and as Steven walks out the front door she stands by that open window. Then when it cuts to the exterior shot, in an instant that window's brown venetian blinds are now down and the white curtains are drawn closed, as Steven walks down the lawn.
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.
Visible crew/equipment: After Russell shows up in the FA/18 with the last missile, when President Whitmore says, "We'll draw them off and it'll be all yours," the set's multiple light tower is reflected on the President's helmet visor.
Continuity mistake: After Major Mitchell is asked get a gun to shoot the Coke can, in shots facing David, the Major's body faces toward the alien attacker, but in shots facing the alien attacker Major Mitchell's body is turned the opposite way.
Continuity mistake: After going to the bathroom, when Steven turns on the TV in the kitchen, in the TV's close-up before the program comes on, the kitchen's reflection is visible. In the reflection something is lying on the stove (beside the fridge) and a chair is in front of the corner door, but when it cuts to Steven opening the fridge door, they're gone.
Continuity mistake: When the spaceships begin arriving, it is obviously morning in Los Angeles. Will Smith and his girlfriend are still in bed, and later on Will goes out to get the morning paper, etc. Jeff Goldblum has just said that the countdown will be over in roughly 7 hours, so how is it night in LA when the spaceship finally attacks?
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 we see the Russian picture of the map where the UFOs are going in their country, the Cyrillic for Petrograd is incorrect as there is a Western lower case "r" in the city's name. The small "r" is close in appearance to the Cyrillic "g" which has a straight line (east to west)at the top of the letter instead of the curved line that we associate with our lower case "r".
Continuity mistake: The alien saucer that arrives over Los Angeles is said to be approaching off the California coastline, yet it is specifically shown approaching from Imperial Valley, which is to the east/southeast of Los Angeles.
Suggested correction: Not true, Constance says, "One is heading for Los Angeles, the other two are on our eastern seaboard heading toward New York, and Washington D.C." No direction of travel is given.
General Grey reported to the President the destroyer (hidden in a fire cloud) was being tracked "off the California Coastline."
Continuity mistake: At the MCAS El Toro ruins, when Steven's chopper is heard overhead, the First Lady sits up and leans on her right arm with her left arm over the blanket. In Jasmine's close-up, the First Lady is lying down fully covered by the blanket, but when it cuts back to the First Lady her position is back as the first shot.
Continuity mistake: When Steven is dragging the alien in his parachute, the sweat stain on his tank top changes shape and gets smaller, by the time he speaks with Russell a few moments later.
Visible crew/equipment: When Russell lands his crop-dusting plane and Miguel rides up alongside on his motorbike. The equipment used to help stop the motorbike, at the right position for the close-up, is visible on the ground - but it's gone in the wideshot. (Only visible on fullscreen DVD.)
Continuity mistake: When the two couples say their goodbyes, before Steven and David's mission, Jasmine has her right arm over Steven's shoulder in the shot facing her, but next shot her right arm is down, under his arm.
Continuity mistake: When Julius and David drive to DC, the amount of dirt on the Plymouth's front and back windshields varies between shots.
Continuity mistake: When the B2 releases the nuke it banks away to the left, however the next radar shot shows it flying away to the right.
