In general, detection is the extraction of information from any clear or clouded ambient or otherwise accessible stream of information without neither support from the sender nor synchronization to the sender.

In the history of radio communications, "detectors" where the first operable type of semiconductor diodes to extract modulated signal from their carrier. Still today, in multi-channel systems, detecting is the selective extraction of an AM signal from its carrier frequency.

In communications, detection is the extraction of intelligence from a carrier signal in a stream of electro-magnetic energy. Note that this may be either an overt signal, as in a conventional radio broadcast, a noise signal as in heavily interfered ambient signals or a covert signal, as in steganography. Typically this involves a radio detector.

In opto-electronic or other radiation systems, the detection means the generation of an electrical signal in response to a received optical input. For example, the optical signal received from an optical fiber is converted to an electrical signal in a detector, often by a photodiode.

In steganography, attempts to detect encoded intelligence from 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 produce the probability of the existence of payload material encoded in the carrier; this is in contrast to the detection of signals which are simply encrypted, as the ciphertext can often be detected with certainty, even if it cannot be decoded.

In the military, detection means the special discipline of reconnaissance with the aim to recognize the presence of an object in a location or ambience.

Finally, the art of detection, also known as following clues, is the work of any detective 1.

See also

• Signal detection theory