Security metal detectors have been used successfully for years to detect even the smallest amount of metal. They are able to detect things as small as a safety pin to large firearms. Although they are designed to detect certain items, some single-zone units function in a way that the entire metal contents on a person are combined and read as one signal.
An interesting thing to note is that U.S. money is printed using a type of metallic ink. So, if a person were to go through a single-zone metal detector with a large amount of cash somehow strapped or taped to their body, they could very well set off an alarm.
Studies were conducted with handheld metal detectors at the University of Washington, which is in Seattle. Physicists found that metal detectors could sense the metallic ink in a one dollar bill from under two inches away. As the physicists increased the size of a stack of bills, the magnetic field increased as well. The larger the stack of bills, the farther away the metal detector could sense them. By determining the magnetic field, the researchers were able to accurately determine how many bills were in each stack.
How Much Did You Say You Had?
While the researchers were able to determine how many bills there were, they could in no way say how much money there was. That is because all the bills have roughly the same amount of metallic ink in them. So if a security metal detector was used to find out if a person was carrying a lot of cash on them, they could never be sure how much it was. There is a huge difference between one hundred $100 dollar bills and one hundred $1 dollar bills.
To date, a security metal detector can’t differentiate between different types of metal, so if a large stack of cash were to go through a metal detector it would merely trigger an alarm. As technology improves, there may come a day when security metal detectors are able to find smugglers trying to leave town. That being said, some metal detectors can already stop loss prevention for precious metals.