>Is that something you actually need AI for though?

Need? Probably not. I bet it helps though (false positives, etc.)

>would be cheaper, faster detection, more reliable, easier to maintain, and more.

Cheaper than the phone I already own? Easier to maintain than the phone that I don't need to do maintenance on?

From a fun hacking perspective, a different sensor & device is cool. But I don't think it's any of the things you mentioned for the majority of people.