Hi there and welcome
It can be a real reading or the device has malfunctioned. As you cannot take this risk, I advise you evacuate the premises, and have the fire brigade come and perform a reading.
When you evacuate, close all windows and doors when the last person has left so that they can properly test if there is a CO buildup.
If they discover there is not, then the device is defective and you would need to have it replaced. But I advise you have this confirmed asap by the fire brigade now and leave the premises.