There are two types of alarm posts, and their in-game text (if you have not seen that) is thus:
Alarm Post:
When an AI Command Station is destroyed on the alarm post's planet, or an adjacent planet, all of the guards at the current planet will desert their posts and go on the attack. If the alarm post itself is attacked and destroyed, there is only a 50% chance of it alerting the guards.
Special Forces Alarm Post:
When an AI Command Station is destroyed on the alarm post's planet, or an adjacent planet, all of the "special forces" ships in the entire galaxy will turn aggressive and attack the humans. If the alarm post itself is attacked and destroyed, there is only a 50% chance of it alerting the special forces ships.
I think that answers all of your questions, but if you had never been in the same system with them, you wouldn't have had that info. That's where the F1 help (that cycles the planetary summary) can come in real handy, when you're encountering new style types.
Let me know if there are more questions, outside of that, though. The CPA disappearing thing was just a bug (should finally be fixed in 3.101), so that's unrelated; sorry for the confusion there.
Hope that helps!