Do these ever get confused by the things that ordinarily screw up compasses? (eg. iron deposits, power lines, metal walls, etc) Firefighters navigating in smo

Do these ever get confused by the things that ordinarily screw up compasses? (eg. iron deposits, power lines, metal walls, etc) Firefighters navigating in smoke-filled buildings could benefit from something that helps them maintain an absolute sense of direction, but guessing that might be too hostile an environment.