Olmstead vs. United States (1928):

Discovery and invention have made it possible for the government, with means far more effective than stretching upon the rack, to obtain disclosure in court of what is whispered in the closet. … The progress of science in furnishing the Government with means of espionage (on American citizens) is not likely to stop with wiretapping.

Ways may some day be developed by which the government, without removing papers from secret drawers, can reproduce them in court.

The makers of our Constitution undertook to secure conditions favorable to the pursuit of happiness. They recognized the significance of man’s spiritual nature, of his feelings, and of his intellect. … They sought to protect Americans in their beliefs, their thoughts, their emotions and their sensations. They conferred, as against the government, the right to be let alone – the most comprehensive of rights, and the right most valued by civilized men. To protect that right, every unjustifiable intrusion by the government upon the privacy of the individual, whatever the means employed, must be deemed a violation of the Fourth Amendment.