By now there's a virtual assistant in most homes (and hands) with Alexa devices, Siri oniPhones and iPads, and "Hey Google" on Android phones and Google devices. All of thesedevices have microphones so are they listening to you all of the time? In short, yes.
The always-on devices and assistants are constantly listening for their 'wake word'. Amazon's Echo devices listen for "Alexa" unless you change it to "computer", or "Echo". iOS devices listen constantly for "Hey Siri" (unless you turn it off) and Android devices listen for the words "Hey Google". So the microphones are always on. If you say something similar to their wake word, or if someone says it on TV, the device begins recording.
What happens to those recordings?
Google says the recordings are saved in your Google account and you can review them by going to your Google account and choosing "data and personalization", then "my activity". Use the filter to select "Assistant". You may see several recordings that say "unknown voice command". These are incidents where Google thought you said "Hey Google". You won't see what was said or be able to hear the recording.
Activities that are recorded were likely heard by someone at Google. The company explains data is extracted from recordings but the information is not tied to anyone's Google account or device. A team of Google employees will then review keywords to improve the effectiveness of Google Assistant.
In those settings, you can delete recordings and turn off the option to record and save interactions.
Amazon also records every time an Echo device believes you said the magic wake-word.
To see and hear what has been recorded you can use the Alexa app on an iPhone or Android device. Select the "More" tab, then "Activity" and "Voice History".
Here you'll be able to filter specific dates and devices. Anytime the device thought it heard "Alexa" it began recording. Select one and you'll hear the recording. Many of those may be someone on TV saying something similar to "Alexa", nonetheless, the recording is saved.
You'll also see several instances of "audio was not intended for Alexa" but it includes a recording of what was being said near the device.
You can delete all of those recordings but I haven't found a place to easily turn off the recording feature.
If you don't want Alexa to hear what's being said you should turn off its microphone.
On iOS devices, Siri only listens for the wake word if you have "Listen for Siri" turned on. Go to your iPhone's settings and select "Siri & Search". If you do turn off "listen for Siri" you'll have to press a button to ask for her assistance.
You can delete all Siri and Dictation History in these settings as well. If you do delete the history Apple says the data has been sampled and sent to its servers but the data is not associated with the iPhone.
Of course, if all of this is too creepy you can turn off the microphones and disable Siri. You'll be on your own. No help from any of these assistants unless you turn it back on.