The free feature update, which has been trialed by a select few over the last few months, turns Echo speakers into security devices when no-one's home by allowing them to listen for key sounds indicating danger or intrusion.
Users need to say "Alexa, I'm leaving" to set Alexa Guard to Away mode, after which the device will listen for sounds like breaking glass and the sound of smoke alarms and carbon monoxide alarms.
According to TechCrunch, Amazon has worked with licensed contractors to break hundreds of different glass windows with different instruments in order to create a wide range of different sounds for Alexa to listen for.
Upon detecting an ominous sound, Alexa sends the owner Smart Alerts via phone notifications. Users can also play the detected sound from the Alexa mobile app or Drop In on their Echo device remotely to find out what's happening.
Alexa can arm a Ring or ADT security system, with the user able to choose to forward Smart Alerts they receive to Ring or ADT. Users with Away Lighting can also use the alert to turn on lights so as to make it look like they're actually home.
For more details about Alexa Guard, check out Amazon's FAQ.