Harrow's vulnerable residents have been given a helping hand against doorstep fraudsters through the Nominated Neighbour scheme.
Rather than opening the door when the doorbell rings, the homeowner or tenant presses a police-supplied A5 information card up at their front window.
The text instructs the caller to visit or telephone a particular friend or neighbour's home to have their identity verified, thereby preventing the resident, who may be worried, nervous or scared, from having to open the door to strangers and possibly falling foul of conmen or distraction burglars.
Headstone South Safer Neighbourhood Team came up with the idea - thought to be unique in the Metropolitan Police - and has been distributing the cards for free during the past nine months across the borough.
PC Neil Jennings said: "Our role as a safer neighbourhood team is to engage with the community and make people feel safe.
"With this scheme the residents don't have to engage in conversation with the callers, who can be very glib and can be halfway in your door by the time they start talking.
"We go round to old people's groups and they all seem to think the Nominated Neighbour scheme is a good idea."