People are being told not to get caught out by alarm companies who claim they offer a faster response than police.
A 78-year-old Sutton woman was contacted by a company that claimed it could offer a faster police response to an alarm than someone she would get by dialling 999.
The woman did not believe the claims and called police to make them aware.
Sutton police said most alarm companies are genuine but some may make false claims in order to make sales including that they offer a better response than police or are linked to police in some way.
Police advice is to use companies affiliated National Security Inspectorate or the Security and Alarms Inspection Board.
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