Developments in technology have created the possibility for law enforcement authorities to use for surveillance purposes devices that are in the hands or private premises of individuals (e.g. smart phones, GPS devices, smart meters, etc.). The extent to which these devices interfere with an individual's private sphere might differ. In the European Union, surveillance measures are considered lawful if they have been issued in conformity with the legal rules and the proportionality principle. Taking a fundamental rights approach, this paper focuses on the information needed for adopting proportionate decisions when authorizing the use for surveillance of devices that are not built for surveillance purposes. Since existing methods of privacy assessment of technologies do not offer the required information, this paper suggests the need for a new method of assessing privacy implications of technologies and devices which combines an assessment of privacy aspects with the different dimensions of surveillance.