Comment by jsingleton

You can get both. I recently bought a twin pack containing one of each. The optical one is marketed as "toast proof" so you can put it near the kitchen and the alpha source one is claimed to be more sensitive.

Radioactive ones are usually cheaper but come with plenty of warnings about not disassembling or ingesting the source. Best to have a mix spread around the home. It's also well worth having a CO alarm if you have non-electric heating/cooking.