At the opposite extreme from remote sensing is what may be called intimate sensing. Modern technologies use the substance of, or emanations from, the human body and its cells and tissues to detect the presence or the identity of a person, track one’s movements, or provide evidence of one’s past behavior.
Such technologies can be applied to, for example, the use of drugs, sexual activities, or exposure to disease. There are new techniques for finding fingerprints, and computer systems that match them against huge banks of prints on file. Biometric security systems can identify a person by hand geometry, voice patterns, retinal blood vessel patterns, or other physical characteristics. Analysis of DNA, the genetic material within all living cells, also can be used in identification. Blood, semen, and other body fluids can be tested for a variety of factors associated with past experience or present performance.