A plunger lock tool is a tool or key designed to work with a rather unique kind of lock known as a barrel lock. This lock is also sometimes called a cylinder lock. The lock itself is quite different than most conventional locks in that it is in the shape of a cylinder. The locking assembly is actually accessed via a small opening in the top portion of the lock. A meter key uses a plunger type device that injects directly into the locking assembly to actuate the lock into a locked or unlocked condition. The design and function of this kind of lock is built in a way that makes it very difficult to pick or break. The locks have become very popular with gas, water, oil and electric companies around the country and even across the globe. New technology is also on the horizon that will use RFID chip type technology making these locks even more effective.