A rash of counterfeit currency in Suffolk has prompted city officials to warn consumers to be vigilant in checking their bills when they receive change for transactions.

Counterfeit bills in denominations ranging from $1 to $100 have become increasingly common during the past three months, according to Suffolk spokeswoman Debbie George. And counterfeiters have begun to respond to detection efforts by making phony bills of increasingly smaller denominations.

“With the advent of new printers, we do get counterfeit bills a lot more than we used to,” George said, noting that there have been 14 reported incidents in the past 90 days, compared to eight in the same period last year.

“What’s unusual,” she added, “is that the bills appear to be smaller denominations.”

During that period, police have intercepted two $100 bills, two $50 bills, five $20 bills, two $10 bills, two $5 bills and one $1 bill.

Since many businesses now use counterfeit-detection pens for bills at the $20 denomination and higher, criminals have begun to make bogus bills in smaller denominations, she said. Those bills are unlikely to receive the same scrutiny as larger ones, and they sometimes find their way back from retailers to consumers, who receive them in change from purchases.

“The public needs to be aware,” she said. “If they get stuck with that money, the chances of them getting their money back are slim.”

That was the situation in at least two weekend incidents in Suffolk, when cashiers notified their customers that the money they were using to pay for their purchases was fake.

In one of those incidents, the customer told police he had received the bogus bill from his employer, George said. The other customer said he had received the bill in change from another business. No arrests were made, she said.

In a third weekend incident, a customer paid for $136 in lottery tickets and $20 in gas using a $100 bill and three $20 bills. The $100 bill was later found to be counterfeit and was turned over to police, along with a video recording of the person who passed it.

Even the city has not been immune to the spate of counterfeits, having received a fake $20 bill in payment last month for a water bill, George said. That bill was later discovered by the bank.

Suffolk police have contacted the U.S. Secret Service, which is investigating the rash of counterfeits, but there is reason to believe the incidents are unrelated, she said, since police usually find bills of the same denomination — and even the same serial number — when a rash of counterfeit money breaks out in a community.

The best defense against counterfeiters, she said, is to pay attention.

“I would certainly recommend that when you get your change, you actually look at the money they’re giving you.”