I am thinking about upgrading the cd/cassette radio in my 2000 s40, I searched the site already but didn't find info I was looking for. I know the alarm is tied into the radio somehow because an led in the radio flashes along with the led on the dash, so what will happen if I install a new headunit? Is that just an extra wire that won't matter or will my car alarm freak out...I've had enough random issues with my alarm already lol.

Craig

 

That is only a Anti-theft for the Radio.
If you loose battery power or unplug the radio you need a code to reactivate the radio.
It is not tied to the alarm.