I don't think it's an accessory but would be very glad *if* that was the case.
I was very bummed out to find that all my accessory outlets power down when I turn my car off. Other models may be different but on my 2011 E93 they turn off which is a bit of a bummer since I used to leave my phone or iPod in my Audi to charge it but can't do the same with the BMW.
Even doing "bad" things like this my Audi's battery lasted 7 years whereas the BMW is having trouble before 2 years.
Granted the old Audi and the new BMW are completely different beasts in terms of electronics.
As far as locking the car, I was really bummed to hear this might or would be required. I have never really locked my convertibles because the cost of a (soft) top was always more than the belongings inside. The hardtop changes that a bit but I sill find it annoying to "have to" lock my car when it's in my garage. I have heard the car wake up several times but I think it was always unlocked and I walked into the garage with the key in my pocket. Walking near the car seemed to trigger the car to wake up. Don't know if the same would happen if it was locked.
On the same lines, I wonder how close is too close for the key. I hang my key about 4 feet from the garage wall and it's another 8-10 feet to my car from that wall. Now I wonder if just having my key so close to the car all night might be causing issues. This really sucks since Comfort Access was *supposed* to make life easier.