SmartThings usually recognizes simple devices but does not display many of the available advanced settings. Custom handlers are pieces of code that allow users to take advantage of all of the advanced settings some of the newest devices offer; this allows you to fully customize the device if needed. SmartThings has been slower with officially integrating new Z-Wave products, so the community fills in that gap by creating custom handlers.
As of December 2018, the new SmartThings app is not complete, though it requires the handler in order to add your Multisiren correctly. Unfortunately, you won't have access to any advanced settings in the new app at the time of writing - it's still a work in progress!
You can take advantage of the advanced settings in the SmartThings Classic app, but you'll have to add the handler first. If you haven't added one before, it's an easy process that only takes a few minutes. It will let you customize the alarm siren duration as well as reporting intervals for the temperature and humidity sensors. And if for some reason SmartThings isn't recognizing the device correctly, the handler can help with configuration.
1. Exclude the device from your network and log in here with the same information you use for your ST app.
2. Click on My Device Handlers in the top menu
3. In the top right corner, click on "Create new device handler" and choose "from code" from the top tab menu. You'll be presented with a blank area where you can paste the code for the handler. Please click on this link to access the code, then copy ALL of the code from the page.
Once copied, paste it into the blank window on the SmartThings page.
4. Next, scroll to the bottom and click create.
5. Now click save, then click publish > for me.
Once you see the handler on your list of device handlers, include the siren using one of the methods listed here.
Let us know if you have any questions about the process! We're always happy to help.