Continuity mistake: When Beck is shot outside the Precinct, from the front view he has no exit wound on his forehead. Yet when he lands on the snow a few seconds later, an exit wound has appeared.
Factual error: In the shot where the laser sights of the assailants come in through the windows and holes in the wall, their angles are far too different from each other. The shooters are standing at a rather great distance from the structure and at more or less the same height. All the laser sights should have more or less the same direction and certainly not make a sweeping motion inside the room.
Continuity mistake: During the entire movie it is snowing heavily. At the very end, when the last shot pans over the city there is no snow anywhere, not even on the trees.
Factual error: Throughout the movie the patches on the Detroit Police officers uniform is incorrect. As is the Sheriff's uniforms from the prison bus. The Sheriff's department patch has a picture of the state of Michigan in the center, not a star. I do not believe that Detroit police officers even have patches on their uniforms.
Continuity mistake: During the outdoor scenes throughout the movie, and most noticeably during the forest scenes, condensation from the actors' breaths appears almost randomly. Sometimes their breaths can be seen in the cold air, and other times not at all.
Deliberate mistake: In the scene where the group finds out that Jasper has betrayed them and then Bishop uses the flash-bang, the group splits up, and Iris and Capra get into an SUV. Very shortly later, when it goes out of control and crashes, you can see a stunt driver in the SUV wearing blue elbow pads and holding onto the roof, before the SUV hits the ground. (Slo-mo may be necessary.)
Revealing mistake: Anna hot-wires the truck so she and Alex can go get help. As they are driving away, tire tracks from the camera vehicle in front of the truck are visible in the snow.
Revealing mistake: There are several problems with lighting and time sequence during the nighttime forest scene at the end of the movie. The tall trees are backlit by a very bright light, obviously studio lamps for they are much too bright to be natural moonlight. And when they emerge from the dark forest five minutes later, it is daylight and the sun is already several hours over the horizon.
Revealing mistake: About a minute into the movie we see Ethan Hawke waking up. He has a tattoo on his left pectoral. He then goes to the sink and mirror and the camera is directly behind him. He drops out of shot and in the same shot reappears in "the reflection" as he splashes his face with water. His tattoo is still on his left pectoral - all he's done is drop out of shot, move forward a few paces, turns around towards the camera and reappear as the mirror reflection. They've forgotten to either flip the image around or put the tattoo on the other side.
Revealing mistake: The snowfall during the forest scene is very fake-looking. Snowflakes change size and brightness randomly, and twirl around in the air in a very unnatural pattern.
Continuity mistake: Sgt. Roenick's facial hair changes throughout the movie. Most of the time it is seen as a scruffy moustache and goatee, several days worth of growth. But in the scene where he tells the prisoners the precinct is under attack by rogue cops, he is practically clean-shaven. And during the scene in the forest, he is sporting a five-o'clock shadow instead of the usual goatee.
Factual error: In the laser sight scene where lasers are coming into the building from all angles, you see the entire sight line of the laser. This is impossible in real life: you will only see the point where the laser hits a solid object - there must be something substantial to reflect off of besides air. There would have to be an incredibly dense fog inside the building to see the entire laser light, and even then it would be intermittent with the changing density of the fog layer.
Other mistake: During the film Ethan Hawke's pills are talked about between him and his evaluator. When you finally see him open his pill container, it is clear that the pills are actually Ice Breakers breath mints. You can see the trademarked "Flavor Crystals" (the dark blue spots on the white mint).
Revealing mistake: Despite complaining of the bitter cold inside the police station, no condensation can be seen coming from the characters' breath.
Factual error: The movie is set in an about-to-be-abandoned precinct station house in an old "bombed-out" industrial section of Detroit. Much is made of this locale throughout the film & exterior shots show surrounding empty factories, warehouses, etc. In the next to last scene, Laurence Fishburne, Ethan Hawke, & Gabriel Byrne have the final shoot-out in a completely wild, 30 year-old growth, lodge-pole pine forest, having walked there in a few minutes from the precinct. In the last scene, rescue workers come "out" of the forest on a rutted dirt road with a very fake-ily pasted on backdrop of the Detroit skyline in the distance.
Continuity mistake: Near the end of the movie when the marked Detroit police car arrives and skids to a stop you can see the marks from a previous take in the "snow".