The Kauai Police Department says there's a rise in fake $100 bills being circulated across the island.
The scary part is that even counterfeit detector pens can't stop them.
There are options besides those pens, but it depends on how much business owners are willing to spend and how much time they have to check each bill that comes in.
Plate lunch businesses deal mostly in cash, so they are victimized by counterfeiters. Once they turn in the fake bills, they're not reimbursed, so it's a loss.
"We're just so busy that we don't really have the time to check every bill. That's why we're kind of susceptible to getting these counterfeit bills," business owner Zachary Lee said.
"We've had it happen one time before on a $20 bill, so now I tell the cashiers to mark any $20 [bill] or higher," business owner Jason Sung said.
Counterfeiters have found a way to beat the pen.
In the latest incidents on Kauai, the U.S. Secret Service says real $5 bills were washed and bleached and reprinted as $100 bills.
Kauai Police and the Secret Service recommend comparing a suspected fake bill with a known real one.
A real one will have a portrait that stands out, while a counterfeit appears lifeless and flat. A real bill also has line that are clear and unbroken.
Also, check the serial numbers to make sure they are evenly spaced and the same color as the treasury seal.
Some businesses have gone with what's known as a bill authenticator.
"It's very simple. It works very well for us. We don't have to worry about taking in a bad bill," business owner Brian Kimata said.
Kimata says this machine can be programmed and spot every flaw in all types of currencies. His machine costs just under $400.
"It checks the bill size, it checks the paper, it checks the magnetic ink, it checks the watermark, it checks the strip, it checks several different things. It'll indicate which one is questionable," Kimata said.
Kimata believes it's well worth the money he paid for it because it checks the bills fast and gives him peace of mind.
The Secret Service says the best way is still to compare the bills side-by-side.
For more tips on how to detect counterfeit money, visit the U.S. Secret Service website.
The first runner to cross the finish line of the 2013 Honolulu Marathon was Gilbert Chepkwony who finished in 2:18:47.
Dry weather conditions made for a great day as thousands of runners participated in the 41st Annual Honolulu Marathon. Those who ran inspired others to participate next year-- while those who cheered from the sidelines helped motivate them to keep running.
KHON2 is learning more about the elderly man who died after being attacked in Chinatown.
83-year-old Mamerto "Eddie" Semana was found on Kukui Street early Wednesday morning not far from where he lived.