Getting to know my
Join Date: Mar 2013
Location: United Kingdom
The secondary beep when you lock the car is to tell you some part of the system has not worked properly. The way to tell which part is as follows - When you unlock the car again look carefully at the dashboard door lock button light and it will flash a certain number of times to tell you which sensor in the alarm system didn't work when you locked it.
I've had same problem on a 156 and my current GT, from what I can deduce, these are standard codes across most of the Alfa vehicle range, here is the list from the GT handbook:
1 flash = one or more doors
2 flashes = tailgate
3 = bonnet
4 = ultrasound interior sensors
5 = abnormal car lifting/tilting (basically car thinks it was towed away!)
6 = tampering with starting cables
7 = tampering with battery cables or emergency key cables
8 = connection line to sensors and siren
9 = at least three of the above!
Once you have identified the faulty sensor from the code, go ahead and investigate the problem area.
FWIW, I also have notice sometimes the beeps are quieter than normal, weird I know but definitely not your imagination!