I've been buying smoke detectors with 10 year non-replaceable batteries. After 10 years, it starts beeping, and you throw the whole thing away.
Don't forget to get a CO carbon monoxide detector, too.
I think even normal, young, healthy adults without CPAP will not reliably wake up in time in before the smoke gets to them. That's one of the reasons smoke detectors are so important.
However, CPAP may make it worse. What the heck, get two smoke detectors and put them in the room where you CPAP.