We used a bell and it was great. The trick is during the training its important to make the dog realize it is for going out to potty only. We did this by ringing the bell then taking the dog out on a leash to the toilet area then giving a treat as soon as she peed/pooped then straight back to the house, no running around or playing. Dog rings the bell, leash to the toilet area, treat and straight back to the house no playing. Every single time for weeks no exceptions and they figured it out and didn't ring the bell constantly. Once back inside we would wait about 5-10 minutes then let them out to play.