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.
Difference between calling at 10% or 110% sound volume lol.
And if someone was to eavesdrop by holding their ear to my car, I’d say that’s a bit suspicious.