Police say heroin traffickers are retreating to the safety of drug dens reminiscent of the opium days. But the new 'divans' are more sophisticated as operators use closed-circuit television and steel gates in their efforts to outsmart police. Recent police operations have closed 35 dens in Kowloon West, the New Territories and on Hong Kong Island, the latest issue of the police newspaper OffBeat reports. Superintendent Simon So Kam-sing, of the Narcotics Bureau, said: 'These are similar to the old dens used for smoking opium, but now they are smoking or injecting heroin. 'Their operation counters police action as addicts who buy drugs must generally consume them there and then. 'The operators know undercover officers will not actually take drugs, so traffickers see divans as a means of deterring police infiltration and undercover operations.' Drug supplies at the dens were kept at a minimum to cut losses during police raids, Mr So said. However, unlike the dealers who sell drugs on the streets, the dens were sitting targets for police monitoring and operations. Addicts also had been more willing to come forward with information leading to the closure of dens, he said.