Yes - I agree, and remote notification of an issue at home has been useful for me in the past. Water leak sensors spotted a problem before the ceiling was damaged badly.
One of the hopes for the HA 2025 roadmap is sensors like fire / flood can be registered in a semantic model allowing an automation to be suggested with options. Sort of auto-detect + blueprint + druid/wizard.
I’m sure we’ll think of more as the classification of entities expands (the main one will probably be suggesting lighting controls with motion sensors in the same room/area).
You can buy aerosol “smoke in a can” that works with optical sensors (don’t think ionisation, and not heat rise) but it was expensive the last time I looked (a RS smoke machine kit is >£1k), and even the cheap(er) cans need a “funnel on a stick” to direct the spray. It was easier to pay a contractor to test and certificate than buy / 3d print the kit.
It is a real shame that Alphabet / Google / Nest has such a short attention span. The Nest detectors offered something new and useful. Let’s hope others like Samsung Smartthings don’t give up so easily.