JEWELLERS have thrown down the gauntlet to thieves on the eve of today's billion-dollar Hong Kong International Jewellery Show, hit hard in the past two years by professional raiders. But metal detectors and X-ray machines, used at this year's theft-free March show, have been canned because of likely ''inconvenience'' to an expected 20,000 buyers and 400 local and overseas exhibitors. Karl Shin Shiu-kau, chairman of a security sub-committee set up this year to counter thieves, said: ''The machines are costly and cause negative feelings among people who do not want their personal belongings checked.'' 'They say they should be treated like VIPs rather than suspected criminals and we believe that this is a reasonable consideration,'' he said. Thieves at the last September jewellery show - which featured precious stones, pearls, jade, diamonds, silver and gold - made off with rich pickings and brought embarrassment to organisers. Three European men escaped with 50 rings worth $500,000 from a stand at the Convention and Exhibition Centre last September 1, while in March last year it is suspected that Yugoslavian gang helped themselves to a US$500,000 (HK$3.86 million) diamond and a $40,000 platinum ring in broad daylight. Mr Shin, managing director of the KK Fine Jewellery company, said yesterday he was supremely confident that this time the four-day exhibition, organised by the Trade Development Council, would be trouble-free. ''We are stressing to exhibitors that they need to pay more attention to their displays and we are 100 per cent confident there will be no problems. But of course there are no guarantees,'' he said. ''We have also changed some of the showcases to make them more durable and there will be guards and video monitors strategically placed. I think thieves will be very disappointed,'' he said. Exhibition insiders estimated the net worth of all the jewellery at the show would top $1 billion. Police in the Crime Prevention Bureau have advised ways of making the jewellery more secure. The exhibition is open to the public only on September 5.