Okay, so maybe this is a tool for writers who live alone. But since that describes me, I have to list a timer among my most essential tools for writing. I couldn't write without one.
When I write, I am lost. I don't know what room I'm in, what country, or even who I am. So it's easy to lose track of all sorts of things, especially cooking. My trusty timer saves me every day. I just set it and I can allow myself to drift away in a flurry of words. And then, before I know it, it calls me back. "Check the beans!" it yells, or "Walk the dog!" (The dog is in another house; there are no visual cues when it's time to take her out. We don't want to forget the doggie.)
Every writer should have a timer, even those who live with others. Surely the other people leave at some point, no?. A timer frees you to write. Get one.