Foot bolts are substantial locking devices that can, like many others, be overcome easily with the proper tooks and knowledge. Foot bolts are slide bolts that are installed along the bottom rail of the door and lock into the floor. These locking devices can usualy be identified from the outside by the bolt pattern just like a slide bolt that locks into the door jamb. To determine if the foot bolt is engaged or not, take a key tool or shove knife and slide it under the door. If the tool hits the bolt, the lock is engaged. This will prevent wasting time on a locking device that is not engaged.
There are several ways to force these locking devices. One of the quickest is using the power saw to cut the bolt. This will be difficult if not impossible unless you have a power saw set up with an outboard blade. As seen in the picture, the outboard blade allows the saw operator to slide the blade under the door to cut the bolt.
If you don't know how to change your saw to the outboard position check this video out. This two minute real time video demonstrates how to perform this modification to your power saw.