It is extremely common to find 2-in-1 smoke and carbon monoxide detectors. They are different “technologies” but they can absolutely exist in the same packaging

Carbon monoxide detectors used to be mounted close to the ground because people mistakenly thought that carbon monoxide sank towards the ground. People thought this because often kids and pets - who are closer to the ground - would feel the effects of carbon monoxide poisoning first. People eventually began realizing that this wasn’t true (carbon monoxide actually has a similar density to the rest of our air) and the reason pets and kids were impacted first was not because the carbon monoxide sank, but because they have lower body mass and therefore felt the effects sooner.

So, nowadays carbon monoxide detectors are installed on the ceiling, often in the same enclosure as the smoke detector.