The EU standard EN 50291 should be met in any case. A CE mark, a TÜV and VdS seal are further quality features. The European standard EN 50291 generally regulates the requirements of electrical CO measuring devices for operation in residential buildings in the areas of construction, test procedures and operating behaviour. If you want to find out more about this standard, you can do so on the website of the German Association for Electrical, Electronic & Information Technologies (VDE). However, the text of the standard costs.. The CE mark indicates that the product complies with the European directives that apply to the specific product. Although this seal is not a test seal but an administrative mark, it still indicates that European directives are complied with. You are probably familiar with the TÜV seal. The TÜV tests technical products neutrally, expertly and independently and certifies products that meet the high requirements. The "TÜV-tested" seal is at least colloquially a seal of quality, but it is relatively rare for CO detectors. A certification of the VdS (Vertrauen durch Sicherheit) damage prevention products of the civil security market as well as guard and security companies. A VdS seal indicates that the product-specific requirements of the CO detector exceed those of the European standard.