How do i hang up politely?

So today, as I am on my way home from work I am talking to my sister. We get through talking about the ins and outs of our day and my commute home is almost finished. I go to my "go-to" goodbye, "I'm pulling into the driveway, I'll call you later." But she then yells "Ohhh you wouldn't believe what the cat is doing!" and as uninterested as I am, I am now sucked into a play by play description of how her cat is playing with a tassel. How can I stop this from occurring in the future without being a total ass?

EDIT: Mom is calling doesn't work... mom is dead.