Does this actually sound an alarm if a glass break occurs?

Hi Sue. We appreciate the time you have taken to ask this question. Yes, the Ring Alarm Glass Break Sensor can send you mobile alerts when the Ring Glass Break Sensor detects the sound of glass shattering in your home, or you can set the sensor to automatically sound your Ring Alarm siren when armed in Home or Away mode. You can learn more about the Ring Alarm Glass Break Sensor here: https://ring.com/support/products/accessories/glass-break-sensor?page=1. If any additional information is needed regarding your question, please reach out to our community. Ring Community is our first peer-to-peer community forum, giving our customers the ability to help one another and share their feedback and experiences directly with Ring. You can find it here: https://community.ring.com/. Thank you, Amilia from Ring.