How do car keys open car doors?
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Old style key: The same as with house keys. The keys have a distinct form that pushes some pins in the keyhole in a certain position, and when all pins are at the right position, the key can be turned, unlocking the door. In cars this happens mechanically or by triggering an actuator (small motor for example).
Keyfob with remote control: there’s sometimes still a key that works following the same principle as above, but there’s also a small radio transmitter (the first ones used infrared light, like classic TV remotes) that sends a code when the button is pressed. The car “listens” and when it hears its own code, it unlocks the door through actuators.
Keyless entry systems: they also have a small radio or sometimes, just an RFID tag (like a radio, but passive, aka only works when its antenna receives power from the car’s own antenna). When you are close to the car, your “key” is in transmission range to the car unlocking the door, again through actuators in each door. For RFID sometimes one needs to be very close, or put the card on a certain spot.
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