Factual error: After the intruders flood the panic room with propane, Jody Foster's character gets a lighter and ignites the propane causing it to burn along the ceiling. This would be impossible as propane is heavier than air and would sink to the floor rather than rise up to the ceiling. Lighting a flame in that room should have caused anyone in the room and on the floor to be engulfed in flames almost instantly.
Factual error: In the scene where Kristen Stewart is flashing SOS in morse code through the hole her mother asks "where did you learn that" she then replies "Titanic." In the movie 'Titanic' they correctly used the proper distress signal of the time which was actually CQD (CQ is Code for 'All Stations' and suffixed by 'D' for distress). CQD in Morse code is -.-. -.- -..
Factual error: When the burglars use the crowbar to break through the roof hatch, the security system display changes from "System Armed" to "Zone 19 Disabled" which can only occur when the zone is disabled by the user. Additionally, the alarm should have sounded immediately when the sensor on the hatch was broken. If the circuit had already been disabled then the security system would not have reacted by saying "Zone 19 Disabled."