A dye pack is a small, hidden security device that banks place inside bundles of cash given to robbers during a holdup. Once the money leaves the bank, the pack explodes, coating the stolen bills (and often the thief) in bright red dye and tear gas. The goal is simple: make the money unusable and the robber easy to identify. In robberies where dye packs activated, about 71 percent of stolen money was recovered, according to a U.S. Department of Justice survey.
How a Dye Pack Is Built
A dye pack is hidden inside a hollowed-out stack of real bills, typically $10 or $20 notes, so it looks and feels like an ordinary bundle of cash. Modern versions use thin, flexible housings that are virtually indistinguishable from real currency. Older models were more rigid, and experienced criminals could sometimes detect them by feel or weight. Today’s packs are designed to fool even someone who handles cash regularly.
Inside the housing sits a small amount of red dye, a tiny explosive charge, and in most models, a capsule of tear gas. The dye is a vivid red compound originally developed for colored smoke formulations and military smoke grenades. It stains intensely and is extremely difficult to wash off skin, clothing, or paper currency.
How the Trigger Works
The pack sits on a magnetic plate inside the bank teller’s cash drawer, keeping it in standby mode. When a teller hands over the money during a robbery, removing the pack from the plate arms the device. At that point, a radio transmitter mounted near the bank’s exit doors does the rest. As the robber walks through the doorway, the radio signal triggers the explosive charge.
There is typically a short delay built in, usually a few seconds, so the pack doesn’t detonate inside the bank and injure employees or customers. The idea is for the explosion to happen once the robber is outside or inside a getaway vehicle. When it goes off, the reaction reaches temperatures around 400°F, hot enough to scorch the surrounding bills and sometimes ignite clothing or the interior of a car.
What Happens When It Detonates
The explosion is small but intense. A cloud of red dye sprays outward, saturating the stolen cash and anything nearby. The dye bonds to paper fibers, skin, and fabric almost immediately. On skin, the stain can persist for days, making it very difficult for a robber to avoid suspicion. On the bills themselves, the bright red marks render them obviously tainted and nearly impossible to spend.
Most dye packs also release tear gas at the same time. This is the same chemical irritant used in riot control. It works by attaching microscopic particles to moist surfaces like eyes, nostrils, and the lining of the mouth. Within 20 to 60 seconds, the exposed person experiences intense burning in the eyes, involuntary tearing, coughing, chest tightness, difficulty breathing, dizziness, and excessive salivation. In fresh air, these symptoms generally fade within 10 to 30 minutes, but inside a closed car the effects are far more severe and disorienting. That disorientation is part of the point: a robber who can barely see or breathe is much more likely to abandon the money, crash a vehicle, or be caught quickly.
Can the Dye Be Removed?
This is what many people are curious about, and the short answer is: not easily. The red dye used in bank packs was chosen specifically because it resists common cleaning methods. On paper currency, removal is essentially impossible without destroying the bills. The dye soaks into the fibers and bonds chemically, and any attempt to bleach or wash it leaves the money visibly damaged and still obviously stained.
On skin, the dye fades over several days as the outer layer of skin naturally sheds, but scrubbing with soap alone won’t remove it quickly. On clothing and fabric, the stain behaves like a permanent dye transfer. Heavy-duty stain removal techniques involving prolonged soaking (eight hours or more) and repeated treatments with oxygen-based bleach can sometimes reduce visible traces on fabric, but the original vivid red is almost impossible to fully eliminate.
Banks and law enforcement count on this persistence. Even if a robber escapes the initial scene, red-stained hands, face, or clothing draw immediate attention. And trying to deposit or spend dye-marked bills at any bank or business is an instant red flag.
Why Banks Still Use Them
Dye packs have been a standard anti-robbery tool in U.S. banks for decades, and the 71 percent recovery rate helps explain their staying power. They serve a dual purpose: they mark stolen money as unusable, removing the financial incentive for the crime, and they produce physical evidence (stained skin, clothing, vehicle interiors) that links a suspect to the robbery long after the fact.
They also function as a deterrent. Robbers who know a bank uses dye packs face a calculated risk that the money they steal will be worthless before they can spend it. Some experienced bank robbers have been known to search through cash bundles looking for packs before fleeing, but modern designs have made this increasingly difficult to do under pressure. The combination of a convincing disguise inside real currency, a radio-triggered delay, and the dual punch of permanent dye and tear gas makes the dye pack one of the most effective passive security measures in banking.