The best friend of the unauthorized entry specialist is the government.
Yes, you heard me right. The government. Two things make a breaking and entering into a business or public office as easy as can be. The first is the "Life Safety Code," which says they must provide free egress 24 hours a day. This means the inside of the door must be able to be opened without a key. The second is the Americans with Disabilities Act (ADA), which mandates that a person in a wheelchair, on crutches, with limited or no use of hands, or just plain stupid can get the door open.
What does this mean to you, the soon-to-be unauthorized-entry specialist? Simply put, if you can’t pick the lock, you can use alternate entry methods. I will show you two of these methods, and you can use your fertile minds to design a few others.
The first idea is to bypass what are called panic devices or crash bars. These are devices that hold the door shut, but when you push on a bar or paddle the door is then able to be opened. They allow for free egress and can be used by a disabled person. These devices are most often mechanical, but some are electronic. The electronic kind will be dealt with later.
Panic devices will most often lead into stairwells or other fire escape routes. You can tell from the outside that a panic device is on the door by the mysterious lack of door knobs or door levers. If the door is able to be accessed externally, there will be a keyed cylinder on the side where the knob should be. Often a handle will be there as well. In many cases, there will be no exterior access available, and this is the "Dead Giveaway," as it can be called.
To get these kinds of doors open you need a device that is thin enough to fit under the door, yet has enough strength and weight to be flipped up at a good bit of speed in order to strike the device, duplicating the force of a human pushing on the bar. The "arm" on this device should be 4 feet long, as building codes demand that panic bars be mounted around 36 inches from the floor. You should have a sturdy, yet thin, hinge fastening the "arm" portion of the device to the "base piece." A lever should be added that will work like the foot peddle for a drum set. This lever should have a 45-degree bend and attach to a fork that fits around the "arm," the idea being that when you stomp on the lever, the "arm" flies up, strikes the panic device, and opens the door. The accompanying illustration shows the basic idea.

A second device is easier to make, and is used to open most lever-type panic devices. The ADA requires these devices to open freely from the inside by anyone, regardless of handicap. Thus a long thin metal rod with a wire that runs the length of the rod can be worked under the door, manipulated upward, and looped over the lever, then pulled down until the door opens. It may sound easy, but you'll need practice to get it right.
Keep in mind that the Fire and ADA Nazis are your friends. With them on your side, no door is really locked. Just watch for alarms. We'll get to them later.