I came home from the shops on a Saturday morning, a few months back, and my wife greeted me with the words, 'Your workshop has been broken into and everything is gone.' I was gutted! I'd been burgled! It was a bit like closing the stable door after the horse had bolted, but I decided that I'd have to make a DIY burglar alarm.

I raced down to the bottom of the garden and the door to my lane was hanging on a hinge and my workshop door wide open. All of my tools had been stolen. My bench saw, planer, hand drills, router, polishers, sander, electric saws, tree lopper, chain saw, even my gardening knife. All gone. When the police came they didn't hold out much hope of catching the thieves or of recovering any of the tools because, they said, the thieves would have already fenced them. But they did give me a very loud and piercing 120decibel alarm to fit to the door, and they warned me that the thieves would be back, after I'd bought new tools.

Of course my mates down the club had the answers: electrify the door knob: rig up an axe so that when they open the door, the axe chops them up: fit a twelve bore cartridge in the vice so that it fires when the door is opened: lay a pressure mat so when they step on it an arrow is released from a crossbow. All good ideas, if a trifle over the top.

I settled for the alarm the police had given me and a back-up alarm of my own device. The police alarm fits on the door at the top and a short link from it fits over a hook on the door frame. When the door is opened, the link pulls out a pin and the alarm goes off. All very well, I thought but if the thieves spot the link, they can just unhook it as I do when I enter the workshop. So I built a back-up alarm, just in case.

First I rigged up a bank of three high wattage spot lights to shine on the door as it's opened, run from the mains power. Then I connected a 12volt car horn to the lights, driven by a mains/12volt transformer. Using a refrigerator's internal switch, the one that brings the fridge light on when you open the door, I connected that to the door frame and ran the cable to the lights/car horn. So that I can get into the workshop without deafening myself, I fitted a switch just inside the door enabling me to open the door a crack and turn it off. When the door is opened by anyone not in the know, the fridge switch pops out and brings on the lights and car horn and the opening door pulls out the link on the police alarm, causing panic and confusion among the baddies.

Well, I'm happy to say that last night the thieves returned. This morning, the alarms were blaring away, the lights shining brilliantly, and nothing had been taken. I just hope their heads are still ringing.