Bump key is a specialised lock-picking tool used to defeat pin tumbler locks through a method known as 'bumping'. This technique involves inserting the bump key, which has been specifically cut to a uniform depth near the maximum of each pin stack, into the lock. When struck on the head with an object like a hammer or screwdriver handle, kinetic energy is transferred to the key, causing the pins within the lock to jump momentarily above their shear line, allowing the lock to be turned and opened.
The design of a bump key is deceptively simple, mirroring the basic form of a key for the targeted lock type but modified to maximise mechanical impact on the pin stacks. Its effectiveness relies on precise timing and the physical properties of the lock components, exploiting small tolerances and defects in the lock design. Bump keys are controversial due to their ease of use and the minimal skill required to operate them, raising security concerns in residential and commercial settings. They are typically constructed from durable materials such as brass or steel to withstand the impact of bumping without deforming.
The use of bump keys poses significant challenges for lock manufacturers, prompting advancements in lock technology, such as security pins and electronic locking mechanisms, to counteract this vulnerability. Despite these innovations, the simplicity and low cost of bump keys make them a persistent threat in lock security.