Around the ignition there is a coil. That sends and reads signals to and from the transponder (not transporter) in the key near the blade. So you really need to hold the blade side of the key in or very near the ignition as the coil won't send a signal for more than 0.5 cm. (or something like that).
As for the remote control: that signal goes up to 50 meters and more. This you can check out how far you can stand away from your California and see from what distance it doesn't react anymore.
The remote signal can easily picked up when closing your California (or opening it) by a device from people with bad meaning.
In crowdy places I try to remember to close my California with the key in the lock in the door. Then they can't read a signal from the remote.
As for starting it, I think there must also be devices to bypass the transponder code, otherwise they can't be stolen without the key.
Unfortunately we drive a car from a manufacturer that is still very wanted to steal. VW, Audi, Skoda, Seat, are from the same family, so once they crack the code, all those vehicles are near to similar to open and drive away without the proper key.
You can't do more than hoping for the best, or try to install anti theft, but whey they really want your vehicle, they will take it, no matter what, unless it really takes too much time, or they are disturbed when trying to.
But, after 9 years, mine has never been stolen (lucky), even with the least effort to really secure it. The only thing I have lying around in the trunk is a stoplock steering wheel lock, but then they would only need to cut the steering wheel, pinch it open and remove that lock.
OK, enough of that negativism. Don't let the thought of one stealing your van spoil your lovely trips and holidays!!