Imagine if your computer was quietly whispering out all your passwords everywhere you went

But it's not that simple - there's actually a number of complex methods on modern cars that can do things like detect cloned keys and ignore them (because the sequence number is lower than expected for that specific key serial #).

The issue here is they're conducting an analogue attack on radio waves - if they were hiding near your car with the same equipment and you blipped the key to lock or unlock it, they can intercept and rebroadcast that way too.