So for the X-fire...simplified steps are?

Check/replace Fob battery > Check/replace car battery > Check/Replace Alarm module


and if you take fuse 9 out, for the alarm...can u still drive? Im assuming you won't be able to start it?

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Sounds like the right sequence to me. I replaced the car battery last year and had just changed the fob batteries a month ago because they were getting weak.
A couple weeks ago the alarm was going off randomly. I just quit locking the doors and had no problems with the alarm for 10 days. I also tried taking out fuse #9 but the lights all flashed which I figured would kill the car battery. So you may have a choice I guess -either disconnect the battery or don't lock the doors.
I bought the alarm siren from Mercedes MB part #A 171 820 25 26 - $148.60 Canadian. Chrysler quoted 282.00 Canadian for #5124443AB (5124443AA was much cheaper but no longer available)
You need to remove the wiper arms and take the cowl piece off to get to the bracket. It has a 13mm nut that comes off from the engine side -the other nut is part of the bracket. You need a T30 security torx (has a hole in the centre)to get the siren off the bracket. The new siren has a male threaded shaft instead of a female thread so you will need a new nut to mount it. I finally found one on an old bicycle seat bracket - worked just fine! Made sure I cleaned all the cowl drain holes before I put it all back together. So now it looks like I have solved the random alarm problem and have the quiet beep when locking or unlocking which is a bonus. Probably only took me 20 minutes including finding the nut.
Needed: puller for the wiper arms, T25 torx for the cowl screws (7) T30 security torx bit and a 13mm socket and a metric threaded nut (same size as the windshield wiper nut).

Hope this helps, Ron