A few comments...
My Catalina 34 MkII has a number of improvements that were made later in the production run. One of the best improvements (because it's virtually impossible to retrofit) is an escape hatch in the aft berth. It's a nice size, and installed in a place that's very easy to access. So in addition to the companionway, I have big enough hatches to escape from the V-berth (easy exit), aft berth (easy exit) and main salon (need to stand on the galley counter, but doable).
I am very concerned about smoke detector selection. A couple of years ago I replaced all the smoke detectors in my home. I didn't want to re-wire all the electrical harnesses, so I just went for the closest current model to what I already had with no thought to what type they were. I now know that they are all ionization type, and am now hearing bad things about poor response to the most common smoldering fires. But the similar photoelectric detector (uses the same harnesses) has HORRIBLE reviews for false alarms. Comments seem to indicate false alarms are worse in places with temperature and humidity extremes, which does not bode well for marine environments. More research to do.
Regarding false alarms, there are different types with different danger levels. The type a couple of you mentioned, where it goes off while you are cooking, is merely a nuisance. You're awake, your boat is lit so you can see, and you're 99% certain that it's just the food that's cooking. The much more dangerous type, which I have experienced, is the one that happens in the middle of the night. You're awakened from sleep, the house/boat is dark, and if the detectors are interconnected than they're all going off so you don't even know where to start. I experienced that happening in my house, and it scares the crap out of you. What's worse, it happened a few days/nights in a row on a couple of different occasions. One time it was in my garage in the middle of a muggy late summer night (a few nights in a row), diagnosed as caused by humidity. The second time it was in my attic during a heat wave, diagnosed as excessive heat. The solution in both cases was to remove the smoke detector and replace it with a heat detector.
The issue here is that smoke detectors tend to generate false alarms in environments with large temperature or humidity swings (i.e., boats). Couple that with the fact that many of us leave our boats in a slip for many days at a time, and this becomes a real issue that could quickly wear out our welcome with our dock neighbors and marina personnel (unless you leave your A/C on all the time when at the dock, which creates other problems).
I'm not going to let this paralyze me from doing something for my boat, but whatever I install, I will probably pull out the battery when I leave the boat until I've built up a lot of confidence that it will not have false alarms.
I'm still not sure what to do with my house. I'd rather have photoelectric detectors, but since I travel ~10 nights a month leaving my family alone, I don't want to get a model that is prone to false alarms.
More research needed.