Eighty years ago today, the April 23, 1938, issue of Radio Guide carried this ad for a midget pocket radio from American Leader, 1606 W. 78th Street, Chicago.  Since it needs “no batteries, tubes, or electrical connection,” it appears to be a crystal set.  The ad promised that you can use it anywhere–“in auto, bed, office, hotel, etc.” and that it’s not a toy.  The set sold for $2.99, and the seller covered the postage on cash orders, or you paid a few cents if sent C.O.D.

I suspect that the antenna and ground connections would get a bit tricky in a car,   But subsequent research reveals that it was a quite attractive little crystal set.  The image below appears at Wikimedia Commons:

The caption of that photo reveals that the headphone is stored in a compartment inside the set.  So as long as you had an antenna and ground connection nearby, the set probably was something more than just a toy.