I started using the bells a few weeks after Lulu came home, so she was around 4 months old. As I stated before, it took her a few weeks to learn learn to ring them herself & we are still working on her ringing them every time she needs to go potty. She gets better each week! The most annoying thing about them is she will ring them just to be let outside to play.
But I take her out each & every time anyway.
Good luck with it!
