Penurious Penguin writes "Your curtilage may be your castle, but 'open fields' are open game for law-enforcement and surveillance technology. Whether 'No Trespassing' signs are present or not, your private property is public for the law, with or without a warrant. What the police cannot do, their cameras can — without warrant or court oversight. An article at CNET recounts a case involving the DEA, a federal judge, and two defendants (since charged) who were subjected to video surveillance on private property without a warrant. Presumably, the 4th Amendment suffers an obscure form of agoraphobia further elucidated in the article."