Harpenden residents are being asked to be wary of security companies who are claiming to have an affiliation with Hertfordshire Constabulary.

Officers from the Safer Neighbourhood Team said there is no such affiliation between any home alarm system company and the constabulary.

Security specialists Secured by Design, who work in partnership with the Constabulary, recommend that if residents are considering buying a home alarm system they should:

• Not make agreements with cold callers on the doorstep or over the phone

• Research the credibility of any companies before approaching them

• Obtain written quotes from at least two reputable companies including the details of any monitoring/call-out arrangements

• If you require an alarm for insurance purposes, make sure the company is acceptable to your insurer before making any agreement

• If you have serious doubts about the legality or sales techniques, contact the police or Trading Standards for advice

Some residents have reported that companies are approaching them and claiming that they are working with police, and that their alarm systems will be directly connected to the local police or fire station.

Often the alarm systems are being described as being worth thousands of pounds, but are being supplied for free as part of a special offer. However the company do not mention that there is a monitoring charge.

In many cases these companies may not be registered to the National Security Inspectorate or The Security Systems and Alarm Inspection Board (the leading certification bodies) or any other reputable trade bodies and may even exaggerate crime figures to encourage residents to buy an alarm.

Inspector Paul Lawrence of the crime reduction unit said: "Our advice is to please be cautious and make sure you are clear what these companies are offering before signing up.

"Gather all the information you can from the person calling you. If you are not happy with their selling techniques or feel the information they are giving is not to your satisfaction, you are advised to refuse any further contact or dealings with them.

"I would like to remind residents that in Hertfordshire crime levels, including burglary, have been falling for more than five years in a row and by more than 14 per cent in the past year.

"Just taking a few simple steps can make your home less vulnerable to burglary. A lot of the homes that are burgled have been singled out by the criminals because they have been left insecure - so ensure any sheds and outbuildings are properly locked, especially if you use them to store valuable garden equipment and other possessions such as bicycles.

"PVCu doors must be locked with a key as well as by pushing up the handle.

"Always keep doors and downstairs windows locked when you are out and you should also fit locks to any upstairs windows that are easily accessible from a flat roof extension, for example."

The companies using these sales techniques have been brought to the attention of Trading Standards.

For more advice visit www.herts.police.uk or report concerns by calling the local Safer Neighbourhood Officer by calling 101.