system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do companies that make things such as drone remotes and car keys ensure that the signals won’t work with other drones/cars?
gpt
Much like a physical key, each remote key system uses a unique code to identify itself.  It was not always like this; in the early days of remote keys, a manufacturer would use a limited number of codes, and it was possible for a key to open a car that wasn't yours.

Today it's typically taken a step further using what is called "rolling code."  Basically, both the key and the car get a copy of the same book, and they each maintain a bookmark.  When the key gets pressed, it transmits the first sentence of the page we're on.  The car checks its copy of the book, says "yup, same as what I've got" and both turn to the next page for next time.