A would-be burglar likes the look of your street. And your house is the target. Even before he walks around it and looks in the windows, he has to check to see if someone is home. So the first move in his tradecraft is to come to the front door, ring the bell, and see if anyone answers. Only then, when nobody answers, will it be safe for him to look in the windows, go around the back, and check the best point of entry. If someone goes to the door, he can just ask 'May I speak to Mr. Smith?' and when told that there is no Smith living there, say he must have the wrong address. The police will tell you that this is standard procedure for almost all burglaries.

But when he approaches this house, and gets within five metres of the front door, he hears the loud bark of an angry German-shepherd guard dog. The barking is intermittent, and the closer to the door he gets, the angrier the dog sounds.

He backs off before he even rings the bell. As he does this, the dog stops barking. If he turns around, the dog barks again. Will he take the burglary further? No way! Other houses without guard dogs make easier pickings.

Any experienced policeman in a burglary squad will tell you that the best home security system for your house is a guard dog. But these have drawbacks for many people. Feeding a guard dog, walking him daily, and all the other attention such a dog needs is not possible for everybody. Some people also object to locking their dogs in the house all day while they go to work, and real dogs also need to sleep!

But this security alarm, actually a wireless-alarm electronic dog is on duty 24/7. Marketed in Australia and New Zealand as 'IntruderShield', he never needs feeding or walking, and never drops his guard. He, or the wireless alarm system he represents, is a product of wartime radar technology.

Traditional burglar alarms have a big drawback - the burglar actually has to break in before they activate. And if you leave your burglar alarm on overnight when you go to sleep, you are likely to set it off when you go to the toilet. So people generally switch their traditional alarms off at night, making it easy for the burglar to clean out the house while they sleep.

IntruderShield is a home alarm system that works with radar technology developed for the armed forces. It is a small, 25cm x 18cm x 18cm box that sends out a beam that can go through brick, wood and glass, and detect movement in a radius up to ten meters from your front door. This home alarm has two adjustments, one for range and one for sound volume, and only needs plugging in to a power point. You don't need to call an electrician and the IntruderShield security alarm can be adjusted to make best use of the position you put it in to. It can go into a cupboard, or just be near your front door, perhaps behind a picture frame or pot plant. Switch it on, and your home alarm system, in the form of an electronic guard dog, is immediately 'on duty'.

Not only that, but if you are home and don't want the aggressive sound of a guard dog, but still want to know if someone is coming to the door, a switch on the IntruderShield home alarm system changes the guard dog to 'sounds of the forest glade' - a singing bird, a croaking frog, and a running brook makes for a soothing, friendly sound, but this unique security alarm still tells you when someone is approaching the front door. A third switch position activates an option, which starts with the sound of the guard dog, but switches to a police siren.