A dye pack is one of the more popular ways to foil a bank robber. The pack consists of real bills (usually $10's or $20's) with a device in the middle of the cash that activates when it is triggered by a radio signal. The activation releases red smoke and red dye from the pack. The transmitter that emits the correct radio frequency to activate the device is usually concealed near the doors through which the robber exits. Dye packs are one of the successful ways the financial industry is fighting back!