Two upgrades you may want

[Stan&Sharon]

Smart Smoke Detector
Now I don't need a ladder to remove the dang battery to stop the noise. I also get automatic monthly battery tests and notification on my phone (and there's an app for the wall tablet)

Water Leak Detector
Very common to have vacuum check valve leak on black tank flush. Now I can know it's leaking when I begin the flush - before the basement and undercarriage fills up with water. (yes that's space themed duck tape)

[RogerR]

I have one of those water detectors at home and it is LOUD. Plus 9 volt lasts for years.

Since it is at home I also have a Simply Safe water detector which saved me twice while out of town by alarming in time to send someone over before damage was done. I highly recommend Simply Safe and would mention that you get a month free if someone refers you.

[Stan&Sharon]

I found out that Leak detector is really LOUD today. Notice on the above photo that I installed the sensor into the vacuum check valve, which caused it to leak! Here is where I have it now.

[Mach1tosh]

We put a "smart" smoke detector in our TT last year. I've been really good in the past at using the fantastic fan in the bath to exhaust bacon fumes fast enough to virtually eliminate the smoke alarm going off.
The new "smart" unit has a button to give an 8 minute window that it won't sound. Very clever indeed.