security. There are various grades but the current British Standard (BS3621:2007) is usually required for insurance purposes. Locksmith Valerie Olifent states that, "The doors of many historic churches still carry an old wooden lock although often you find that a modern 5-lever mortice lock has been installed alongside it to meet insurance requirements." BS3621:2007 requires a bolt throw of 20 mm rather than the 14 mm of the earlier British Standard. Most BS3621 locks have anti-pick devices built in to reduce the chance of lock picking, along with hardened bolts and anti-drill plates to reduce risk of physical attack. Vulnerabilities Lever tumbler locks can be picked with a tool called a curtain pick which is inserted into the keyway of the lock, and a force is applied to the locking bolt. The pick is then used to lift each lever inside the lock to the correct height so that the locking bolt can pass. Higher security lever locks (such as the five-lever) usually have notches cut into the levers. These catch the locking bolt and prevent it from moving if picking is attempted (similar to the security pins in a pin tumbler lock). The Chubb detector lock is a variation of the lever lock which was designed to detect and prevent picking attempts. Lever locks can be drilled, but usually a template or stencil is required to mark the drilling point, as the lock mechanism is commonly mortised into the door and so it is harder to determine the point at which to drill. See also Warded lock Mortise lock Lock picking References Locks (security device)