A US court OKd warrantless use of hidden surveillance cameras, saying police can install such cameras on private property without obtaining a warrant. U.S. District Judge William Griesbach ruled it reasonable for Drug Enforcement Administration agents to enter rural property without permission, and without a warrant, to install multiple \"covert digital surveillance cameras\" in hopes of uncovering evidence of marijuana being grown, CNET reported Tuesday. In the case in question, defendants Manuel Mendoza and Marco Magana of Green Bay, Wis., had sought to have video evidence thrown out on Fourth Amendment grounds. Griesbach adopted a recommendation by U.S. Magistrate William Callahan that the DEA\'s warrantless surveillance did not violate the amendment, which prohibits unreasonable searches and requires warrants describe the place that\'s being searched. Callahan based his reasoning on a 1984 U.S. Supreme Court case in which a majority of the justices said that \"open fields\" could be searched without warrants because the Fourth Amendment does not cover them. \"The Supreme Court has upheld the use of technology as a substitute for ordinary police surveillance,\" he wrote. Mendoza and Magana had argued \"No Trespassing\" signs were posted throughout the heavily wooded, 22-acre property owned by Magana and there also was a locked gate.