https://www.theverge.com/2018/9/20/17883428/amazon-alexa-guard-alarm-ring-smart-home-security-price

Amazon is adding a few new features to the Echo that turn it into one of the basic pieces of a smart security system. Since Echo speakers are always listening, they’ll be able to start listening for the sound of broken glass, or for a smoke or carbon monoxide alarm to go off. If it hears those sounds while you’re out of the house, it’ll be able to send a notification to your phone; or, if you have a supported professional monitoring system, send it directly to the service monitoring your home.

The feature set is being called Alexa Guard. It won’t be working at all times — instead, you’ll have to enable it when you leave the house, by telling Alexa that you’re leaving. Once you do, it’ll start monitoring and be ready to send you alerts.