My Alfa 155 lives on the drive just outside my bedroom window. At 2:30 this morning the horn (not the alarm) decided to sound continuously. After regaining conciousness and deciding that World war 3 hadn't in fact started, I threw on some clothes, ran outside barefooted in the rain, opened the bonnet and ripped off the battery connect.
OK, you can stop laughing now.
As most of the town will testify to Italian horns are very loud. eek!
I've no idea what caused this, but the rain water dripping into the cabin might be a clue.
Italian electrics strike again!
I'll have a look today, perhap the water has dripped on to the steering wheel and activated the horn relay
Rest assured I will be removing the horn fuse every night for some time!
sounds like a poor earth connection under the bonnet,look around under the bonnet for a bunch of black wires all connected together joined to the chassis somewhere clean up all the contacts and see what happens.