Where can I get a device to transcribe writing telepathically?

Here’s the details. I’m a writer. I’m constantly thinking up new stories, but I’m usually either on the bus, or at work. I’d considered a miniature digital voice recorder to read my story aloud, and then play the recording back into something like Dragon Naturally Speaking that evening to produce a text file that I can edit. But I can’t do that on the bus, because I write erotic/thriller/horror stories, and people around me will think I’m criminally insane. What I really need is a device that will simply let me think my story into a text file, and then edit it later when I get home. Does anything like this exist?