I have a 1998 1.6 GSi corsa, the battery went flat and was removed and placed on charge.I have now placed it back on but the alarm is activated causing the horn to sound for 30 seconds when i open it up etc.The hazard light is flashing to indictate it as alarmed and the manual tells you how to switch it off but not to reset it, if it as been activated.
Are you opening the car with the key in the lock or with the remote?
If you're using the key the alarm will always sound.
You have to unlock the doors with the remote to switch off the alarm.