Two elderly sisters thwarted a bogus caller in Hollingdean when he said that he needed to turn off their water supply during roadworks.
The vigilant pair – both in their late eighties – watched the man throughout this visit.
He called at their home in Crestway, Brighton, at about 10.30am on Wednesday 23 March, although it has taken some time for officers to establish the facts relating to the incident.
The pair let the man in but followed him around their home until he left.
PC Duncan Lloyd, of Sussex Police, said: “We would like to hear from anyone who thinks they recognise this man or has been approached in similar circumstances.
“Although the sisters did let him in, they did keep an eye on him, and needless to say there were no roadworks outside.
“Preferably, keep unknown callers out, but if they do get in, watch them like a hawk and if in any doubt call us via 999.”
The man was described as white, in his forties, of large build, 5ft 10in tall and with dark hair.
He is thought to have been wearing a dark boiler suit.
Anyone with information is asked to call 0845 6070999.