Don't Lockout Your Car Stereo
Newer model vehicles have a security feature with their audio/navigation systems. If you lose power to them you may have to enter a security code, otherwise your device will be unusable! Dealers are supposed to have this code entered for you in a sticker either on the inside of your glove box or inside your auto manual.
I typical scenario would be having your car starter battery die and have to be replaced. Your new battery is plugged in and you expect everything to work as before only you find out that you're presented with a strange screen on your stereo asking for numeric code. We recently dealt with this on our new 2012 Honda Civic Hybrid. It developed a starter battery problem, so the battery was disconnected in order to diagnose the issue. I already knew I needed the security code, and found a code inside the glove box, but it was not labeled for what it was for. I called a Honda 800#, provided them with the vin, and verified that the label was for the stereo. One interesting bit of information I also learned was that for this model Honda, a code is NOT needed, even though one is provided for you. All you have to do when presented with the screen to enter the code is turn off the stereo for 2 seconds, then back on.
If you have the option to wait before disconnecting power to your radio/navigation system, I urge you to verify that you either have the security code or there is a similar means to bypass the code as I found for our vehicle.