* Unlocking the doors: If the alarm is *actively* sounding, you'll first need to unlock the car's doors using the key in the driver's side door. This will often stop the horn, but might not disarm the system completely.
* Professional assistance: A locksmith specializing in automotive security, or a Cadillac dealership, will likely have the equipment and expertise to either disable the alarm system or bypass it. They might be able to program a new remote for you, but that may require proof of ownership.
* Disconnecting the alarm (Not Recommended): You could potentially disconnect the alarm system's battery or fuse. This is strongly discouraged, as it’s a complex system and improperly disconnecting components could cause damage or create other issues. Furthermore, it removes a crucial security feature of your vehicle.
In short, there's no simple, DIY solution to operating the 1991 Cadillac Sedan DeVille's factory alarm system without the remote. Your best bet is to seek professional help.
