The little things like fixtures, plug covers fire alarms, etc.

This is in context of a smoke alarm interconnection for R-3.1 (residential care facilities)

The only thing that is alarming is a wet spot beside a window.

I don’t know anything about CO, but around here, converted duplexes don’t require anything special other than smoke alarms.

I don't think you'll be missing something with either choice. 99% of what I end up doing is with pretty basic stuff: e-mail, browser, maps, flashlight app (amazingly handy), camera, weather apps, calendar, productivity (pages, numbers, and keynote, the iOS equivalents to word, excel and powerpoint), calculator, kindle app, iBooks (mostly to capture .pdf documents), banking apps (from your bank), open table (restaurant reservations), trip advisor app (handy for finding stuff near you, though the map apps are pretty good at this, too), airline apps (flight status, online checkin), clock (haven't used a watch in years, also for timers, stopwatch, and alarm functions), pandora, fandango, flash seats (concert tickets), and a few others.These phones are really handy when traveling.

It was wintertime, with snow on the ground...the very loud alarm went off, and when I checked the property I could see footprints walking around to the back of the house, where they entered.

You might be able to get a discount on insurance but most of the time thats for burglar alarm system and fire alarm system with a certificate from the licensed company.

Once I saw water in the crawlspace , alarm bells would have went off . 

. :-) I like that I can also control the thermostat, arm/disarm the alarm (and clear accidental fire alarms) remotely on my cell phone.

We use Ecobee just tt simplify a few things on our STR's that I am near enough to that I stop in if something is wrong, I added moisture and temp range alarms as well as occupancy alarms to the unit, it also allows me to turn heat up or down remote.