How to add an extra camera to my baby monitor?

Sarahbear621

We have a summer infant day/ night video camera that I LOVE.  DS will be 15 months when DD is born so we just want to add another camera- our current one is capable of adding it, but I'm not sure if we need a specific camera for our current model of will any summer infant do.  Does anyone know?  I have no idea what model we have and I don't see it listed on Amazon anymore.