I just saw a headline about Ford patenting a system to eavesdrop on passengers conversations to serve them related ads. If I had patented that before, could I stop it from being used?
In theory yes
In reality, they will find a way around your patent.
Look up the patent on window wipers as an example
This oddly reminds me that the original patent for the chainsaw was for aiding childbirth.
I’ll let anyone curious enough google that.
In theory yes, you have to remember though that you have to enforce parents yourself. If you suspect infringement you will have to sue and carry the lawyer costs, at least until a court judges in your favor. This is off course besides the costs of applying for the parent itself. Your patent might also not be valid in all countries.
In practice the chances of a private person doing this and winning against a multi-billion dollar corporation without going bankrupt are negligible.
Those damn parent application costs!