It's not cheap, but I know of an excellent device you can check
at www.x10.com, called PA5800 System. It has a POWERFUL horn,
and is activated by remote control, and is capable of calling
automatically up to 4 telephone numbers!! I think it costs about
80 dollars. The only problem with it, in my opinion, is the remote's
activation button being a bit hard to push.
Phone numbers:
USA: (201)784-9700
1-800-526-0027
Canada:
(416)624-4446
1-800-387-3346