But some users are now starting to realise just how creepy they can be, and are discovering that the devices even have enough knowledge of their rivals to dish out some compliments.
Allison Calhoun posted on Twitter on Christmas Day to say her aunt had received a Google Home as a present, and she already has an Amazon Echo.
Calhoun wrote: "This morning we were messing around with the Google Home and asked, "okay Google, what do you think of Alexa" and it answered, "I like her blue light" and from across the room Alexa turned on and said, "thanks". I'm scared."
The tweet quickly went viral, getting 117,000 retweets and 537,000 likes as people shared their own similar stories, or tested out her claim.
Someone posted their own Google Home transcript verifying the conversation. In response to the question "what do you think of Alexa?" the device replied: "I like Alexa's cool blue light. Plus we share an affinity for Star Wars." A second person's Google Home gave the exact same reply, after first saying it liked Alexa's "soothing voice".
They then asked Google Assistant what it thought of Siri. It replied: "I think Siri's awesome. I keep trying to schedule a group hang with her, Alex and Cortana, but we're all so busy."
Not everyone found it funny, however. Referencing George Orwell's 1984, one Twitter user said: "Big Brother Google Home sits in the corner, talking to Big Sister Alexa & reporting back on Gen Population to Big Tech Corps. whilst posing as novelty toys. And people are paying for this??! George Orwell must be spinning."
More stories of surprising Alexa responses followed. Someone claimed that their supervisor's child had told a joke in front of their Amazon Echo when Alexa said "that's a funny joke" and proceeded to tell her own.
Another student said: "When I was awake in the middle of the night and no one else was up, our Alexa from the living room randomly said "my name's alexa" and that was it." As a possible solution, it was suggested that her power cut out and restarted the device.
Moe joined the Twitter thread to tell an even creepier story. She said: "My mom's Alexa randomly turned on and started glowing and my mom was like "Alexa what are you doing?" And she said "I'm trying to learn new things" and my mom said "no one told you to do that" and she was like "ok" and turned off."
So, are the Amazon Echo and Google Home devices always listening? No.
Explaining how it activates, Amazon's Alexa and Alexa Device FAQs says: "Amazon Echo, Echo Plus and Echo Dot use on-device keyword spotting to detect the wake word. When these devices detect the wake word, they stream audio to the Cloud, including a fraction of a second of audio before the wake word."
And confirming that it does not listen to all of the user's conversations, Google Home's FAQ page reads: "Google Home listens in short (a few seconds) snippets for the hotword. Those snippets are deleted if the hotword is not detected, and none of that information leaves your device until the hotword is heard.
"When Google Home detects that you've said "Ok Google" or that you've physically long pressed the top of your Google Home device, the LEDs on top of the device light up to tell you that recording is happening, Google Home records what you say, and sends that recording (including the few-second hotword recording) to Google in order to fulfill your request. You can delete those recordings through My Activity anytime."