Astra G Alarm System?

With recent problems with the alarm system, now fixed (new power sounder). I have been trying to figure out the operation of the alarm.
With 1 press of the key fob, the doors lock and the alarm looks like it arms. LED on dash comes on for 10secs and then starts flashing.
With a 2nd press on the key fob within 10secs of the 1st, there is a sound from both doors and the indicators flash again.
Book says 1st press should be only the Central Locking and the 2nd press is the alarm.

Can anyone confirm?