When you use your car’s built-in speakerphone feature, the speakers in the car door reverberate, sending the sounds outside of the car. Maybe don’t do this while your car is parked. Everyone in the neighborhood or store parking lot can hear your very intimate or business-related conversation.
There’s this talk, where researchers found major US cellular networks decrypting people’s conversations at the tower then broadcasting them unencrypted to the entire continent via satellite:
https://media.ccc.de/v/39c3-don-t-look-up-there-are-sensitive-internal-links-in-the-clear-on-geo-satellites