Every electrically operated, data-processing device emits electromagnetic radiation. This applies equally to analogue telephones and electric typewriters, for example, as well as to electronic devices of all kinds, including photocopiers and fax machines, and to all IT devices such as monitors, computers, routers, etc. This is unavoidable due to fundamental physical laws.

For the protection of confidentiality, the critical parts of the radiation of a device that processes confidential information are those that contain "clear", i.e. unencrypted, information. These components, from which CI information can be reconstructed, are called compromised emissions. Whether a potential attacker can siphon off usable information from it depends largely on the intensity of the compromised emissions at the attacker's location.

Emission testing is always a risk assessment in which suitable measures for minimising risks of compromise are determined according to certain criteria. These criteria are laid down in the National Zoning Model of Emission Security, an overview of which is given below.