What is "dye pack"

n. A hidden explosive device with an mass of distinctive paint, intended to stain stolen goods like paper money to make them too distinctive to use without being identified.

A dye pack is a radio-controlled incendiary device used by some banks to foil a bank robbery by causing stolen cash to be permanently marked with dye shortly after a robbery.

In most cases, a dye pack is placed in a hollowed-out space within a stack of banknotes, usually $10 or $20 bills. This stack of bills looks and feels similar to a real one, with technology allowing for the manufacturing of flexible dye packs which are difficult to detect by handling the stack.

When the marked stack of bills is not used, it is stored next to a magnetic plate near a bank cashier, in standby or safe mode, ready to be handed over to a potential robber by a bank employee. When it is removed from the magnetic plate, the pack is armed, and once it leaves the building and passes through the door frame, a radio transmitter located at the door will trigger a timer (typically 10 seconds), after which the dye pack will safely deploy and release an aerosol (usually of Disperse Red 9) and sometimes tear gas, intended to destroy the stolen money and mark the robber's body with a bright stain. The chemical reaction causing the explosion of the pack and the release of the dye creates high temperatures of about which further discourages a criminal from touching the pack or removing it from the bag or getaway vehicle. Dye packs are used in over 75% of banks in America.