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.
Regardless of which app you're using, 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.
You should now see this device type in your list of device handlers. Now you can include the multisiren to your SmartThings hub using one of the methods listed here.
New SmartThings app users: once the handler is installed and the device is included to your SmartThings network, click on the multisiren in your app and tap the 3 dots in the top right corner of the app. Then tap Settings. There you'll be able to customize your device.
Classic app users: once the handler is installed and the device is included to your SmartThings network, click on the multisiren in your app and click on the gear icon in the top right corner to access the device's advanced settings. There you'll be able to customize your device.
Let us know if you have any questions about the process! We're always happy to help.