I was working on the Disco today, in the rear hatch area, when all of a sudden the horn went off. Turning the ignition on did nothing, so I removed the fuse for the horn. The hazards kept going, so I wound up just disconnecting the battery since the car isn't ready to be drive anyway.

Does this have to do with the alarm bypass issue? Could someone explain that a bit further to me? Neither of my keys have a keyfob. And right now, my driver's side door lock does not work at all. Is that how central locking is activated?

I've had the car about a month, and this is the first time the alarm has gone off, so I'm a little confused by it all.

 

I don't have a key fob either but to disarm the alarm I just have to unlock the drivers side door. Even though your lock does not work if the cam is still present to hit the microswitch that is in the locking mechanism it should disarm the alarm. Also try turning the key 3 times to the right as I have heard that disarms the alarm too but am not certain that is true.
The drivers side door is how the alarm is set.
I don't know why your alarm randomly went off nor do I know what alarm bypass means.

 

CLEARLY this is just a case of your high tech LR alarm detecting approaching invisible ninjas. Our rovers were built with such great sophistication and timeless quality tech that we simpletons cannot even comprehend the sheer awesomeness. Just accept that you are safe now and coulda been dead if that horn didn’t scare off those trained assasins and pay no mind to the fact that now your vehicle will not start for ANY apparent good reason....

 

I gave all of that a try, and I'm still locked out.

I've read about bypassing the alarm entirely by grounding a pin, but I have zero idea what that means. Are there any more detailed write-ups on this, preferably with photos?

 

Yep, typically seasonal issue.

Not seasonal by any stretch of the imagination

There is a sticky at the top of this forum regarding an alarm bypass. I'll admit I haven't read much of it as it doesn't apply to my truck.

And now I see that you have already found it. Good luck!