What does 'Hco' on the LCD display mean and what should I do?
'Hco' on the LCD display means the carbon monoxide concentration has exceeded 550 PPM, which represents a very dangerous level. All people must immediately leave the premises when this reading is shown. The display concentration range is 10–550 PPM (±10%), and anything above 550 PPM triggers the 'Hco' warning.
From the official Airam 7126612 Carbon Monoxide Alarm Detector manual, page 3
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