I believe that leak detector uses the same API as the newer Honeywell WiFi thermostats. There is a community integration for those thermostats. See this thread: [RELEASE] Beta 1 - version of Honeywell Home Thermostats (Lyric etc...)
It would take some work, but you could reuse the code for discovery, authorization, etc. and just create a new device for the leak detector. You would have to poll it, though, as events are not supported by the existing Honeywell Home App/driver. The REST API used by this App/driver is documented here: https://developer.honeywellhome.com/
I have a fork of the original code that I am using to fix bugs, as the original developer is no longer supporting it. It is here: GitHub - tyuhl/hubitat-honeywell-Maintenance: Fork of thecloudtaylor's Hubitat Honeywell Driver/App for Ongoing Maintenance
