I didn't have to look far to replace my combo CO/Smoke detector or do a ton of hard searching to find one that just took a 9-volt. The first two results on Amazon US for "smoke detector" take 9-volts.

> The first two results on Amazon US for "smoke detector" take 9-volts.

I did the same thing, and the first four results were Kidde and First Alert Smoke Alarms with non-replaceable 10-year lifespan batteries.

It is likely because you recently purchased one, and Amazon has targeted your results based on your purchase history.