Alfa romeo 156 how disengage alarm spare key will not deactivate alarm by remote only unlock doors manually?

To disengage the alarm on an Alfa Romeo 156 using a spare key, try inserting the key into the driver's door lock and turning it to unlock the door. This often deactivates the alarm. If that doesn't work, you may need to disconnect the battery for a short period to reset the alarm system. Additionally, check the vehicle's manual for specific instructions related to the alarm system.