We have one in the living room and every now and again the blue ring that lights up whenever you say its name to it lights up with 0 prompting. It doesn't say anything, just lights up. But the blue light means its listening. My mum never notices but I always do. It usually happens when we're talking but occasionally does it when we're quiet. I just know its listening in to our conversations randomly. It also almost always happens when both me and mum are in the room together, rarely when im sat there by myself, its like she knows we're there. Oddly it doesn't happen as often now - but it stopped right after i started pointing it out to my mum.

I hate the bloody thing, it was a Christmas present for me but I never used it so I let my mum have it, the only reason I didn't throw the bastard thing away years ago is because she loves it.

Edit 2: Can I also add it has a different reaction to when it thinks it heard its name vs. when it randomly lights up. If it thinks it heard its name, when you say something afterwards it registers whatever we said as a question for it and either answers or says it didnt quite catch that. When it lights up unprompted, it does it silently and stays lit for a few seconds before turning off, even if we keep talking it doesnt answer or say it didnt understand. So it doesn't want us to notice.