A dye pack is a security device used in banks and financial institutions to deter and track criminals who attempt to rob or steal cash. It is typically a small, electronic device that is placed inside a bundle of banknotes and activated when the bundle is taken from the premises without authorization.

When activated, the dye pack bursts and releases a colored dye, usually red or green, staining the banknotes and any nearby objects with a permanent color. This makes the stolen money easily identifiable, discouraging criminals from using or passing it on. The dye is also difficult to remove, making it challenging for thieves to launder or clean the stolen banknotes.

Dye packs are an important security measure in crime prevention and the recovery of stolen money. they are often accompanied by other security features, such as GPS tracking devices and alarms, to further deter criminals and assist law enforcement in apprehending them.