I have two identical shake flashlights I got at an open air market.
One of them has a magnet that slides inside a coil, which feeds a standard small diode and a tiny 25mAh NiCd battery. I can shake it and use it any time I need it.
The other one looks like it has a magnet that slides inside the same coil. But the coil wires aren't connected to anything and the "magnet" is just plain iron. It has a CR2016 cell instead of the NiCd battery. I didn't have to shake it, but it only worked for a few hours.
The boxes they came in look the same, even the same words are spelled wrong. The flashlights look the same unless you really look closely.