An example of a product classified according to its function is a carbon monoxide (CO) detector. If the CO detector captures and displays gas measurements, then it is properly classified under subheading 9027.10, which provides for "Instruments and apparatus for physical or chemical analysis (for example, polarimeters, refractometers, spectrometers, gas or smoke analysis apparatus; instruments and apparatus for measuring or checking viscosity, porosity, expansion, surface tension or the like; instruments and apparatus for measuring or checking quantities of heat, sound or light (including exposure meters); microtomes. Gas or smoke analysis apparatus". If the CO detector does not capture and display gas measurements, then it is properly classified under subheading 8531.10, which provides for "Electric sound or visual signaling apparatus (for example, bells, sirens, indicator panels, burglar or fire alarms), other than those of heading 85.12 or 85.30. Burglar or fire alarms and similar apparatus".