When is radio code useful?
 

Yesterday I forgot to turn off the light and the battery was depleted enough that it is no longer able to start the car. (But the instrument panel was still lit up.) So I charged it all day today and started it. To my surprise, everything works just fine. I lost some settings, but I was able to use the radio etc. Can somebody educate me what is the use of the radio code? I was going to input it somewhere, but it seems unnecessary.

It doesn't take much battery power to sustain the radio's memory. It looks like the battery wasn't completely dead since your panel still lit up.

You might try yanking the radio's fuse and waiting an hour or two to see if it demands the code when it's turned back on.

As a public service...

I took the battery out and charged it using my Battery Tender. So I am sure that the car has no power for about 12 hours.

Must be an optional code :)

Edit: Since it's a theft deterrent, the need for the code is probably triggered by removing the unit from its wiring harness -- nothing to do with the car battery. Why don't you give that a try...

Most car stereos have a few hours of internal battery backup built into them. This allows the car to have no power (dead battery, being worked on/serviced) without the loss of clock and radio settings.

Many times while switching out batteries or working on the car with the battery disconnected will cause you to use the radio code.

I removed the Optional Bespoke unit and let it sit for months in a closet. I installed it into another car and it worked with no issues and without asking for a code.

I would also like to know what the code is used for. Maybe it only applies to the base level head units.