Alexa, smartphones and Co. - monitoring every spoken word?

One or two years ago I recognized personalized ads on google and Facebook for things I never looked up at google.

I wasn’t sure if there was a connection between my conversations with my family and the personalized ads, so I made some tests with my son:
We had a fake talk about buying a pool for a few minutes, and the next time I went on Facebook I had lots of ads for pools and equipment on my timeline. It was winter. So no pool-season in Germany.

We repeated this test several times with different things, but the result was always the same.

I don’t really feel comfortable with the idea, that my microphone is monitoring every spoken word.

Has somebody of you recognized further things than personalized ads?