# Detection

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Being seen by someone or something

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In general, **detection** is the action of accessing information without specific cooperation from or with the sender; it is "the fact of noticing or discovering something".[1]

In the history of [radio](/source/Radio) communications, the term "[detector](/source/Detector_(radio))" was first used for a device that detected the simple presence or absence of a radio [signal](/source/Signal_(electronics)), since all communications were in [Morse code](/source/Morse_code). The term is still in use today to describe a component that extracts a particular signal from all of the [electromagnetic waves](/source/Electromagnetic_radiation) present. Detection is usually based on the [frequency](/source/Frequency) of the [carrier signal](/source/Carrier_signal), as in the familiar frequencies of [radio broadcasting](/source/Radio_broadcasting), but it may also involve filtering a faint signal from [noise](/source/Noise), as in [radio astronomy](/source/Radio_astronomy), or reconstructing a hidden signal, as in [steganography](/source/Steganography).

In [optoelectronics](/source/Optoelectronics), "detection" means converting a received optical input to an electrical output. For example, the light signal received through an [optical fiber](/source/Optical_fiber) is converted to an electrical signal in a detector such as a [photodiode](/source/Photodiode).

In [steganography](/source/Steganography), attempts to detect hidden signals in suspected carrier material is referred to as [steganalysis](/source/Steganalysis). Steganalysis has an interesting difference from most other types of detection, in that it can often only determine the [probability](/source/Probability) that a hidden message exists; this is in contrast to the detection of signals which are simply [encrypted](/source/Encryption), as the [ciphertext](/source/Ciphertext) can often be identified with certainty, even if it cannot be decoded.

In the [military](/source/Military), detection refers to the special discipline of [reconnaissance](/source/Reconnaissance) with the aim to recognize the presence of an object in a location or ambiance, either literally (for example, enemy forces massing on the border) or by extension (as in a defense system or [computer system](/source/Computer_system)).[2]

In [medicine](/source/Medicine), medical devices can provide detection for medical conditions, such as heart conditions by a [stethoscope](/source/Stethoscope), or the detection of seizures in premature babies.[3]

Finally, the art of detection, also known as *following clues*, is the work of a [detective](/source/Detective) in attempting to reconstruct a sequence of events by identifying the relevant information in a situation. In [law enforcement](/source/Law_enforcement), it is "the fact of the police discovering information about crimes".[1]

## See also

- [Detection dog](/source/Detection_dog)

- [Object detection](/source/Object_detection)

- [Signal detection theory](/source/Signal_detection_theory)

## References

1. ^ [***a***](#cite_ref-DicDef_1-0) [***b***](#cite_ref-DicDef_1-1) ["detection; noun"](https://dictionary.cambridge.org/us/dictionary/english/detection). *Cambridge University Dictionary*. Retrieved 25 November 2025.

1. **[^](#cite_ref-2)** ["Enhanced Maritime Biological Detection System Provides Biodefense Capabilities for Sailors"](https://www.army.mil/article/289197/enhanced_maritime_biological_detection_system_provides_biodefense_capability_for_sailors_in_near_real_time). *United States Military (Department of Defense)*. Retrieved 25 November 2025.

1. **[^](#cite_ref-3)** Taylor, Nick Paul (25 November 2025). ["Ceribell wins FDA clearance for seizure-detection algorithm in neonates"](https://www.medtechdive.com/news/ceribell-clearance-seizure-detection-neonates/806376/). *MedTechDrive*. Retrieved 25 November 2025.

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