Children's novel about a boy who buys a device from an old man and travels to a parallel universe

Question

I'm trying to remember a book I read in the late 1970s. It was about a boy who goes to this wild old man's shop and buys a device (I remember it being kind of like a transistor radio). When he uses the device as he's walking along he unexpectedly shifts into a parallel universe. I seem to remember something about lizard people and perhaps motorcycles, but I could be wrong about that. Any thoughts?

Thanks!

Answer 1

Per Phil's (own) comment, the book described is "Alan Mendelsohn, The Boy from Mars" by Daniel M. Pinkwater