Excuse me if I present another side to this story.

It is possible that the mechanic looked in your owner's manual packet and found the radio code (it came with my Volvo on an official-looking card in the owner's manual packet), and decided, reasonably, that he had all the information necessary to disconnect the battery. It is possible that, only after he disconnected the battery, he determined that the code belonged to another radio.

In other words, the scenario you presented does not demonstrate that the mechanic was a moron. It just means that XXXX happens!

I am of the opinion that the OWNER is EQUALLY responsible for knowing that the radio has a code--it is clearly discussed in the owner's manual, which is the responsibility of every owner to read.

It is annoying to hear someone point the finger at someone else when the person doing the pointing shares responsibility.

As for getting the code from the serial number--I hope not. What good would the security system be if anyone and everyone could translate the code from a serial number. Even if that translation is available from the dealer; it should only be available to the registered owner of the vehicle, upon proper identification. These radios pop out in seconds, literally. I wouldn't my radio walking into a dealership in the hands of some teenager, who, with a little fast-talking, would walk out with my fully-functional radio.