Inventor David Auty is confident his newly-launched burglar alarm will go with a bang when it reaches the shop shelves.

When an intruder triggers his ingenious Site Sentry device, it automatically fires a blank shotgun cartridge, scaring off the would-be thief and alerting its owner.

Mr Auty, 54, has worked on the project in his Yeadon garage since November, responding to a cry for help from friend Stuart Petit, of Rawdon, who was at his wit's end following countless thefts from land where he keeps horses.

The inventor said: "I needed a simple mechanism that was low cost and easy to fix up with no electricity. I got a 12-bore blank cartridge, no different from a banger, and fixed up a mechanism in a cash box from which something could drop and strike the pin to set off the bang. It is effective, simple and it works."

Within the top of the device is a ball bearing which sits on a piece of metal with a tiny hole in it. Once it is armed, the slightest movement causes the ball to drop and hit a pin into the cartridge which then explodes.

Mr Auty said he took great pains to ensure that the device , which has a patent pending on it, could only be used upright, had no movable parts and could not be converted into a weapon.

But he said he was not inspired by recently-released farmer Tony Martin, who was convicted of shooting dead a teenage burglar at his isolated Norfolk home.

"I have taken a belt and braces approach to make it absolutely safe and legal," he said.

"There is no shrapnel, no springs or triggers, so it cannot be modified into anything else."

And Mr Petit is thrilled with the results. He said the Sentry had been triggered once since being installed and the intruder had quickly fled empty-handed.

He said: "I had feed, horse jackets, even a horse trailer stolen. I was fed up, but David came up with this thing.

"I have two of the sentries now and haven't had a burglary since. It frightens them senseless."

"There is very little that householders can do to protect their home within the law, but this is marvellous."

Site Sentry costs £199 and will be in the shops shortly.