Our battery powered Carbon Monoxide detectors (CO alarms) warn you of carbon monoxide with a very loud alarm sound and offer an LED or digital display. They are covered by 5, 7 or 10 year manufacturer's warranties and all of our alarms, as a minimum requirement, comply to the latest British Standards (BS EN50291-1:2010+A1:2012).
There are largely two alternative ways for a carbon monoxide alarm (CO alarm) to display the presence of dangerous levels of carbon monoxide:
LED warning lights together with an alarm siren
Digital display of actual CO concentration readings and an audible alarm when dangerous levels are reached.
CO detectors with LED display will only trigger an alarm at over 50ppm (number of CO molecules per million air molecules), a level that ignores the damaging impact of long term lower concentration exposure, believed to be somewhere around 20ppm. This limitation is unfortunately cast in iron by a British Standard.
CO detectors with digital display, while still only audibly alarming at over 50ppm, will at least display the actual CO concentration, even at very low concentrations such as 10ppm. Some of them, for example the CO9D detector, will even allow you to read the maximum concentration of CO the detectors has measured since the last query by pressing a button.