At Amazon’s Alexa event last month in Seattle, the company teased a new feature soon coming to its voice assistant: the ability to whisper. The company demonstrated how whispering a request – like “play a lullaby” – to Alexa would trigger the voice assistant to respond in kind. Today, Amazon says Whisper Mode is officially going live.

The feature is now rolling out to users in the U.S., the company tells us, and works in U.S. English.

It’s particularly useful around bedtime or nighttime scenarios, where you’re trying to keep the room quiet. And, of course, it’s especially helpful for parents, who don’t want to wake a sleeping child to command Alexa, or who are trying to set a more peaceful “bedtime,” “nap time,” or just generally “quiet time” tone to their interactions.

Whisper Mode is one of several features Amazon has been working on to make Alexa more context aware.

For example, the assistant knows that a command to “play Hunger Games” likely means launch the movie, if asked on a device with a screen, while the same command to an Echo speaker would start the audiobook instead.

Also at Amazon’s September event, the company showed off a forthcoming smart-home feature for Echo devices called “Alexa Guard.” This sound-detection technology will allow Alexa to recognize smoke alarm, carbon monoxide alarms, and the sounds of glass breaking.

Both Alexa Guard and Whisper Mode use a machine-learning network known as a “long short-term memory,” explained Alexa head scientist Rohit Prasad.

The incoming audio signals are broken into ultrashort snippets, and the long short-term memory network processes them in order, the company explained in September. The system also factors in its judgments about preceding snippets when trying to make a judgement as to whether a new snippet is a whisper or alarm. In this way, it can learn systematic relationships between segments of an audio signal that are separated in time, Amazon says.

The company also showed off last month how Alexa voice interactions were becoming more natural through “context carryover” – meaning you could ask follow-up questions, like “how about tomorrow?” after first asking “will it rain today?”, for example.

And recently, it patented tech that would allow Alexa to tell if you’re sick, then offer to sell you meds – like cough drops. The system could also detect emotion, like joy, anger or sorrow, according to reports.

To check to see if Whisper Mode has reached your Alexa device, you have to enable it.

Whisper is an account setting, so it needs to be turned on in the Alexa App under Settings (Alexa Account -> Alexa Voice Responses -> Whispered Responses.) Whisper Mode can also be enabled by voice, simply by saying “Alexa, turn on whisper mode.”

Correction, 10/18/18, 12:30 PM ET: This report previously said there was not a setting to enable Whisper Mode. But there is. The article has been updated to reflect this information.