Remembering the home phone number

I have noticed some changes to my mother’s memory. It’s obvious to me, because I live with her, but other people probably wouldn’t notice. I’m not sure whether or not it is going to get any worse. But it’s got to the point where I’ve started to worry about her when she goes out for a walk, because if she got into some trouble, or got lost, I know she won’t remember our home phone number. My strategy for this is writing our number boldly on a piece of paper and taping it to the back of her phone. Doing little things like that give me some peace of mind.