This is my son Fallon’s shoe, a Skecher’s Hot Lights Chopper, U.S. size 12.  The toe, filled with LED lights, is glowing in the picture. It has been blinking at me from across the room all evening now. It reminds me of the heart of a shark I once saw beating on a dock in Boothbay Harbor, Maine, hours after it had been cut from the fish. Unlike that shark, Fallon’s shoe isn’t dead, but it is getting close, the flashes coming further and further apart.

Light-up shoes are a fact of life for American parents.  Fallon, who is four, is in the golden age of light-up shoes and he loves them.  But I gave little thought, until tonight, to how such flashing shoes work.  Kids ask, of course, so I always gave them my best guess.  Strontium-90 energy packs were out of the question since the 1950s, I explained, so the only mechanism that made sense to me was a piezoelectric crystal generating a small voltage with every step.

But this single Skecher, mocking me from across the room, showed I was wrong.

My theory of shoe operation required walking to generate power to light the lights, yet here was a sneaker lighting-up all by itself for hours and hours.

A little research on the Internet and I had it and you can too if you are willing to buy 5000 pieces at a time — the LED light controller and battery from a child’s light-up shoe (below).  I guess piezoelectric crystals cost more and batteries cost less than I thought.

And for the geekier parents reading this, yes, that’s a mercury cell in your kid’s shoes.  Two of them, actually.