Could not find anything on this on the Porsche forums but found in other German car forums:
Faulty hazard light fuse/switch
Faulty trunk/hood latch that is setting off alarm when jolted.
Horn not sounding due to low battery as alarm sounds.

My battery was on life support before kicking. Thinking that was a bad idea.
Looking forward to update, still very bad idea to drive this car with a bad cell, can damage alternator from what I read.

 

I just experienced today (10/12/12) this issue on my 2007 997. I unlocked the car via the fob and the blinking stopped. Re-locked with fob and no blinking.

I replaced the original battery just a little over a year ago (9/4/11) with an Interstate MTP 94R. Anyone have a yet-to-be-posted follow up on this thread, or suggestions?

 

Happened to me as well today. Blinking stopped when I used the key lock/unlock button. Noted that my e-pass had fallen off of the window (held in place by suction cups which let go). Could it be related to the internal motion sensor? I'm also on the original battery, so it may be time for replacement.

 

This happen to my 997tt back in October 2012. Dealer could not find anything but they did have to replace one of my horns. So, I am just now wondering is something had set of my car alarm but the horn was broken so I did not hear anything???

 

New battery and no more false alarms for me. PDK even shifts smoother with the new battery.