A covert listening device, more commonly known as a bug or a wire, is usually a combination of a miniature radio transmitter with a microphone. The use of bugs, called bugging, is a common technique in espionage and in police investigations.
A borescope is an optical probe, or “snake cam,” inserted through a small hole drilled into a wall, or other crevice that lets an investigator inspect and explore a small portion of the wall without causing extensive damage. Also good for covert video surveillance.
Biometrics refers to technologies that measure and analyze human body characteristics, such as fingerprints, eye retinas and irises, voice patterns, facial patterns and hand measurements, for authentication purposes.