I found this alarm detector on amazon which would be cheaper than replacing my interconnected fire alarm system. I checked the database but didn’t find it listed and was wondering if I searched wrong.
if this is not supported is there any device like this that is?
Zwave devices are supported as soon as someone buys one and adds it to the database.
So I guess you will be the one 
Are you sure you just want an audio detection?
If you have some sort of dry output contacts on your existing system you could buy one of those universal zwave binary inputs:
That’s an interesting device - by listening for the sounds of a fire alarm, it completely avoids the quagmire of national legislation, building regulations, insurance sign-off and as you say might be cheaper than replacing an existing system.
Connecting to an existing system sounds simple, but all of the domestic interlinked detectors I’ve seen in the UK have different and proprietary 3rd wire or now strange RF signalling. Sadly, even industrial fire alarm panels seen to prefer 24v ‘state change’ outputs to plain relay contacts.
An audio interface feels like unnecessary over-engineering, but it has excellent isolation both electrically and legally! 
Oh I definitely wouldn’t consider it protection of any kind - but here in the US fire alarms are supposed to produce Sound at a set frequency range and set volume range. So it’s not hard to make the logic for it and it should be fairly reliable. (If installed properly)
I want something like this to alert me when I’m gone and to trigger a rule to turn on all lights to make getting out the house easier in a fire.
I’m using Kidde battery powered wireless interconnected.
My issue with the idea of using a contact on the alarm is that the alarms are only standardized on one area. Alert frequency and volume. So what happens in a few years when I need to replace my alarms? Suddenly I don’t have a contact that I did before or the contact voltage has changed. If it wasn’t for that I wouldn’t even consider audio detection.