I know this is an old post but today I applied a simple solution for the problem described above.
One option might be to use the Utilitech Siren on the lowest sound setting (it has 2, the lowest being 80 decibels) and have it activate for 1 second when triggered by the door opening or whatever.
I've done it with a Rule Set and it works well.
You can setup the Rule to chirp for 1 second, wait X seconds and chirp again as many times as you want. Even add a more significant pattern, 3 short chirps, wait 5 seconds, 3 more chirps for garage door, 1 chirp for backdoor, etc.
A little loud, but not bad, and pretty brief, costs $29 and can be used as the standard Alarm/Siren/Strobe for the rest of the system.
Ideally I'd like to see the Aeon Siren with multiple sounds working with the Almond+.