My 05 Escape "non-hybrid" alarm also went off, when my wife was at home alone and she couldnt get it to shut-off. It kept honking for about 30min. She called me and by the time I got home the horn had burned out. The alarm finally shut-off too.
Took it in and the dealer couldnt find anything wrong?? They replaced the horn and hasn't happened since. That was about 6 months ago....