US Patent 9140063 Switch ladder sensor for roll-up door

A system and method for detecting damage to a door system by detecting the presence or absence of a magnetic source attached to the door system for stopping motion or reversing motion of the door to prevent any further damage to the door system. For example, a roll-up type door may be damaged by a vehicle and pulled from its vertical support guides; detecting this event causes stopping of any motion of the door, such as opening or closing the door.