A conman got into a woman's house in Sheffield by claiming there was a gas emergency and he needed to turn her radiators off.
The crook targeted at 74-year-old woman in Retford Road, Handsworth.
An investigation into the incident has been launched.
A South Yorkshire Police spokeswoman said: "These incidents are becoming more frequent.
"The most important thing to remember when answering your door to callers that you don't know is don't let them in until you are sure that they are genuine.
"Do not keep all your cash in the house. One of the reasons bogus callers target older people is because of their tendency to keep substantial amounts of cash in the house. Deposit your money into a bank or building society instead.
"When dealing with an unexpected visitor, Help the Aged urges older people to follow the simple 'Lock, Stop, Chain, Check' doorstep safety advice. Firstly, make sure all outer doors are locked, then stop and think if you expecting anybody, always put the door chain on and look out of the window or spy hole to see who is calling before opening the door, then ensure that you check their identification.
"Genuine callers will not mind waiting for you to make these checks.
"Do not let anyone enter your home until you are completely satisfied that the reason for calling is legitimate.
"When you need to have some work done, always get at least two or three separate quotes from different trades’ people, and never be pressured into parting with money on the spot or signing up to anything you are not happy with."