ELI5 Car Keys - could my remote open someone else’s car?

Is it theoretically possible that my key could unlock a second car somewhere else in the world? Why is the keyless entry system separate to the keyless ignition system? What is an immobilizer? What is a rolling code, and why is it important that my car has one?   ... We explain like i'm five!   Thank you to the r/explainlikeimfive community and in particular the following users whose questions and comments formed the basis of this discussion: miichiseboss123, matraxia, hands_on_tools, dragonx254, donaldpshimoda, slightlylesshairyape and raresh985 To the ELI5 community that has supported us so far, thanks for all your feedback and comments. Send us an e-mail: [email protected]