Dye pack

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A dye pack is a device used by banks to foil bank robbers non-violently.

Banks put dye packs in money given up during robberies. The dye pack is an incendiary device that explodes in a shower of colored ink (usually Disperse Red 9), and sometimes tear gas, intended to permanently stain the stolen money and the robber's hands with a bright red color. Before the pack is used, it is stored next to a magnetic plate that keeps the pack dormant. When it is removed from the magnetic plate to be put into a money bag, it becomes armed. Within the pack is a small radio receiver that receives a signal sent by a transmitter at the door. This activates a timer that causes the pack to explode some short time later, such as when the criminal is in his getaway car.

The design of a modern dye pack is available via US patent #5196828[1].