Stick Up Cam Siren?

Hi all From what I have seen on Youtube reviews and reading articles online, the Stickup cam (which I have just purchased from Amazon UK) has a siren. But I cannot figure out how to enable it in the Ring app. Do you need to have the full alarm system before the siren option becomes available? I was hoping it was something which could be manually enabled on the camera if you were viewing and saw an intruder etc? Or possibly something which could automatically trigger if the camera detects motion. Am I wrong? Im sure the camera does have a siren because I've watched this youtube video review which shows the siren working: [https://www.youtube.com/watch?v=A4F5JZluO74](https://www.youtube.com/watch?v=A4F5JZluO74) Any advice appreciated!