The Chicago Lock Company was the first to come up with this type of lock. It is a classic example of the race toward better security. Certain tension wrenches allow uninterrupted picking using ball picks. You can also use a standard tension wrench or small screwdriver and place it at the center of the keyway. To eliminate unnecessary baggage, use a diamond pick, reversing it to encounter both top and bottom wafers.
The last tumbler in this type of lock is located less than one-half of an inch in. The picking procedure may have to be repeated more than one time-top wafers, then bot- tom wafers, top, bottom-back and forth. Yet these locks are easier to pick than most pin tumblers.
Locate the last wafer on the top side and move it to its breaking point. Do the same with the other top wafers. Keep the tension wrench firm, remove the pick, turn it upside down (if you are using a diamond or homemade pick), and reinsert it to work the bottom wafers. You may have to repeat this process a few times, but double-wafer locks can and will open with such treatment. Schlage has a doorknob lock that opens this way, but the last tumbler is about one and one-half inches in.
Double-wafer locks are easy to master if you have learned to pick pin and wafer tumbler locks. Since double- wafer locks are more compact, you have to compensate for the fact-slightly closer tolerances. These type of locks are used on old pop and candy machines, gas caps, cabinets, etc.