Earlier quoted context omitted.
> Another aspect of older people (and again: Parkinsons and Alzheimers in particular) is a loss of the sense of smell. Which may mean that odors otherwise noticeable and addressed aren't. I highly suspect you hit the nail on the head here from personal experience: My grandma no longer has any sense of smell (or taste, actually) at all. I recall at one point discovering a particularly pungent smell was caused actually…
I've directly encountered the gas-hob-on-but-unlit scenario myself with someone whose sense of smell is virtually completely gone, and it terrifies me. (How far gone? They are unable to distinguish, or detect, the sents of various Dr. Bronners soaps, directly before them.) And mercaptan[1] (the oderising component in municipal natural gas) is among the most detectable scents in existence. The reasons why it was intro…
You can get natural gas alarms cheaply e.g. on Amazon. Since natural gas is lighter than air, they should be mounted above the hob area.