Are your devices always all ears?

How many times has this happened that you would've had a conversation about this particular thing and the next thing you know is all your social media apps and web browsers are displaying advertisements related to it. It almost feels like a nexus. It's not even an exaggeration when I say sometimes, I am shown ads of things I've just thought about in my head. The main question that pops up is whether our so very smartphones are listening to us? The vulnerability begins with voice assistants always having their ear at us with the "always-on" feature to pick up words like "Hello Siri" or "Alexa" or "Ok Google".