proof" lock system that Sargent invented in the late nineteenth century. Such locks are manufactured by only a few companies worldwide. The locking system is supplied to the vault manufacturer preassembled. Many safe-cracking techniques also apply to the locking mechanism of the vault door. They may be complicated by the sheer thickness and strength of the door and panel. Installation The finished vault panels, door, and lock assembly are transported to the bank construction site. The vault manufacturer's workers then place the panels enclosed in steel at the designated spots and weld them together. The vault manufacturer may also supply an alarm system, which is installed at the same time. While older vaults employed various weapons against burglars, such as blasts of steam or tear gas, modern vaults instead use technological countermeasures. They can be wired with a listening device that picks up unusual sounds, or observed with a camera. An alarm is often present to alert local police if the door or lock is tampered with. US resistance standards Quality control for much of the world's vault industry is overseen by Underwriters Laboratories, Inc. (UL), in Northbrook, Illinois. Until 1991, the United States government also regulated the vault industry. The government set minimum standards for the thickness of vault walls, but advances in concrete technology made thickness an arbitrary measure of strength. Thin panels of new materials were far stronger than the thicker, poured concrete walls. Now the effectiveness of the vault is measured by how well it performs against a mock break-in. Manufacturers also do their own testing designing a new product to make sure it is likely to succeed in UL trials. Key points include: It is based on using "common hand tools, picking tools, mechanical or portable electric tools, grinding points carbide drills, pressure applying devices or mechanisms, abrasive cutting wheels, power saws, coring tools, impact tools, fluxing rods, and oxy-fuel gas cutting torches". A breach is a hole in the door or wall of at least 96 square inches (6 × 16 in (15.24 × 40.64 cm)) or breaking locking bolts to allow the door to open. Considers only the time actually spent working (excludes setup, rests, etc.) Does not cover attacks with a thermal lance or explosives. UL-608 makes no claims as to the fire resistance of the vault. Applies to the door and all sides. The lock, ventilation, alarms, etc. are covered by