shackles split apart and come together to lock and unlock. There are two basic types of padlock locking mechanisms: integrated & modular. Integrated locking mechanisms directly engage the padlock's shackle with the tumblers. Examples of integrated locking mechanisms are rotating disks (found in "Scandinavian" style padlocks where a disk rotated by the key enters a notch cut into the shackle to block it from moving) or lever tumblers (where a portion of the bolt that secures the shackle enters the tumblers when the correct key is turned in the lock). Padlocks with integrated locking mechanisms are characterized by a design that does not allow disassembly of the padlock. They are usually older than padlocks with modular mechanisms and often require the use of a key to lock. The more modern modular locking mechanisms, however, do not directly employ the tumblers to lock the shackle. Instead, they have a plug within the "cylinder" that, with the correct key, turns and allows a mechanism, referred to as a "locking dog" (such as the ball bearings found in American Lock Company padlocks) to retract from notches cut into the shackle. Padlocks with modular locking mechanisms can often be taken apart to change the tumblers or to service the lock. Modular locking mechanism cylinders frequently employ pin, wafer, and disc tumblers. Padlocks with modular mechanisms are usually automatic, or self-locking (that is, the key is not required to lock the padlock) Types Combination Combination locks do not use keys. Instead, the lock opens when its wheels are lined up correctly to display the correct combination. A padlock was invented by John I. W. Carlson in 1931 (a patent was granted in November 1934) that has both a combination on one side and a key on the other. Electronic Electronic padlocks are categorized as either "active" or "passive" electronic padlocks. Active electronic padlocks are divided into rechargeable electronic padlocks and replaceable battery electronic padlocks. The key of this type of electronic padlock is no longer a key in the traditional sense, but is unlocked through mobile phone Bluetooth, NFC, and fingerprint. Unlike active electronic padlocks, passive electronic padlocks do not require electricity which makes their use environment more extensive. The passive electronic lock can be unlocked with an electronic key which needs to be programmed. Steel cable Steel cable padlocks have a wider range of uses than padlocks because they have a variable length of