WATCH out shoplifters and handbag snatchers. A successful York inventor has devised a way of outwitting you.

If trials being carried out from Monday on Andrew Gray's revolutionary Safe Or Sound (SOS) gadget are successful, it could be marketed worldwide to the tune of tens of millions of pounds.

Mr Gray, of Beadle Garth Copmanthorpe, devised Safe Or Sound as a way of preventing shoplifters from simply walking off with pushchairs and prams from London's John Lewis store. But it has much wider uses.

Usually stolen or tagged goods are detected by sensors in shop doorways which trigger shop alarms, by which time it is often too late. The thief hurries away into the shopping crowds or passes it on to an accomplice who vanishes into the throng.

Try stealing an item fitted with one of Mr Gray's radio wave-powered gadgets, though, and an amazing thing happens.

If, for example, a John Lewis shopper wheels away a pram, it will at first bleep-bleep a warning that he or she has strayed outside a five metre zone. Bring it back and it will shut up.

But continue outside the zone and head for the door and the pram will then emit a constant ear-piercing screech and continue even in the unlikely circumstance that the thief dodges security staff and gets through the exit.

"It could also be attached to handbags with a matchbox-sized transmitter in a pocket so that any handbag snatcher will find that their haul literally screams for help as soon as they move out of zone.

There are numerous applications and the product could be worth tens of millions of pounds in the market place."

Mr Gray and his firm, Gray Matter, are already regarded with awe by 1,500 supermarkets all over the world, including 750 in the UK which use his other invention, the Radlok.

This is a device which "freezes" the wheels of trolleys it senses being removed from the supermarket grounds.

Since it took off in 1999 it has saved supermarkets chains up to £40 million in lost trolleys and replacements.

Mr Gray, a former pupil at St Peter's School in York, said: "The SOS device is only about four-and-a-half inches across and so it is obviously no good for use on smaller items like razorblades and shoes, but it is ideal for such things as bicycles, golf bags or prams."

Updated: 11:05 Tuesday, February 01, 2005