The callers, posing as grandchildren, pretend they have been detained by law enforcement because of an accident or to pay a fine and ask the seniors to send money to get them out of custody, Lieberstein said.
The callers also tell the senior to wait by the phone for a second call from an attorney, bail bondman or law enforcement officer who will tell the senior where to send the money.
That caller then tells the scam victim to wire the money to a specific place, usually a Western Union station.
Once the money is wired, it cannot be traced, Lieberstein said.
The callers often call early in the morning or late at night to catch people off guard.
The Napa County District Attorney's Office is recommending people who receive such a call ask a question only a family member could answer.
Anyone with caller ID who receives scam calls asking for money should write down the numbers and report them to police, Lieberstein said.