I use a bell, and the one that I have is from a dollar tree and it is really a Christmas decoration. It is just a big bell with a large ring on the top that fits over the doorknob. Any type of bell will work, even a small cow bell or goat bell from a tractor supply, attach a string to it and put it either on the door or as the above poster suggested on the wall near the door.
karen, mom to:
ace-gsd (bi-color) 6/14/2010
mandy-yellow lab 1/31/2009
baby-terrier mix (waiting at the bridge)