Personal security risk?

What are some ways to find out if I am being monitored? I have had some of my phrases repeated to me, from my partner, who wasn't present during these conversations. These are not the usual talks I use but some obscure things I have mentioned in conversation to colleagues and even to my child. I know that my conversations were not shared by them. I thought there was some kind of listening device but had my car checked out, and was told there was no such device in my car or cell phone, which I left in the car. What other methods can be done to tap into my conversations?