Can i use an external tuya smart switch with the osi security system to trigger an alarm horn? if so, what would the communication be between the systems?

The OSI alarm system has an SOS button that you can press within the Smart Life app which will sound the siren(s). All of our systems include a hard wired siren, and some of them also include a wireless siren. Keep in mind that you can add multiple of our OSI-ALM-SIR-W wireless sirens (ASIN# B08RVSYL3F) to all of our alarm systems throughout your home or business, and they will all sound at the same time once you press the SOS function within the app. In addition, there's an SOS button on the main panel, and on the supplied remotes that will also sound the siren(s).

To answer your question, you cannot use an external tuya smart switch with the OSI security system to trigger an alarm horn. I'm sure you can use the tuya smart switch to trigger a separate alarm horn if wired correctly, however we think the solution that's included with our alarm system as stated above, is a much simpler and more effective solution.