{{Unreferenced, date=March 2018
In general, detection is the action of accessing information without specific cooperation from with the sender.
In the history of radio communications, the term " detector" was first used for a device that detected the simple presence or absence of a radio signal, since all communications were in
Morse code
Morse code is a method used in telecommunication to encode text characters as standardized sequences of two different signal durations, called ''dots'' and ''dashes'', or ''dits'' and ''dahs''. Morse code is named after Samuel Morse, one of ...
. The term is still in use today to describe a component that extracts a particular signal from all of the
electromagnetic waves
In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visible) lig ...
present. Detection is usually based on the frequency of the carrier signal, as in the familiar frequencies of radio broadcasting, but it may also involve filtering a faint signal from noise, as in radio astronomy, or reconstructing a hidden signal, as in steganography.
In optoelectronics, "detection" means converting a received optical input to an electrical output. For example, the light signal received through an optical fiber is converted to an electrical signal in a detector such as a
photodiode
A photodiode is a light-sensitive semiconductor diode. It produces current when it absorbs photons.
The package of a photodiode allows light (or infrared or ultraviolet radiation, or X-rays) to reach the sensitive part of the device. The packag ...
.
In steganography, attempts to detect hidden signals in suspected carrier material is referred to as steganalysis. Steganalysis has an interesting difference from most other types of detection, in that it can often only determine the probability that a hidden message exists; this is in contrast to the detection of signals which are simply encrypted, as the ciphertext can often be identified with certainty, even if it cannot be decoded.
In the military, detection refers to the special discipline of reconnaissance with the aim to recognize the presence of an object in a location or ambiance.
Finally, the art of detection, also known as ''following clues'', is the work of a
detective
A detective is an investigator, usually a member of a law enforcement agency. They often collect information to solve crimes by talking to witnesses and informants, collecting physical evidence, or searching records in databases. This leads th ...
in attempting to reconstruct a sequence of events by identifying the relevant information in a situation.
Signal detection theory
Detection theory or signal detection theory is a means to measure the ability to differentiate between information-bearing patterns (called stimulus in living organisms, signal in machines) and random patterns that distract from the information (ca ...
