You mean CO sensor. CO2 is carbon dioxide, a component of the air we breathe.
I have these kiddes. Great that they ade combined co2 and smoke detectors. The version i had was 10 year. I never changed the battery. I did chuck it after 10 as the co2 sensor is meant to deteriorate by then. I bought a new one and it screws directly into the same plate. So no drill needed.
Bs kitemark otherwise don't waste your money.
Not sure how this compares, but went for a Kiddie combined smoke and carbon monoxide detector off Amazon for a couple of pounds more (up to £20.25 at the moment, but I paid £17.60 two days ago so guess it will go down to that price again). Kidde 10SCO Combination Smoke and Carbon Monoxide Alarm with Voice Notification https://www.amazon.co.uk/dp/B00M1Q70K4/ref=cm_sw_r_apan_i_JC4ZD8ZR5DDPDZS1T0NK?_encoding=UTF8&psc=1 Still hot from me though for people only wanting a carbon monoxide alarm.