ebay - cardamatic

[Fred Cisin]

> >Nope. Plastic card (credit card thickness, or less) with
> >pencil-sized holes in it. The "reader" is a matrix of electrical
> >contacts. You shove the card in it, it insulates the non-punched
> >contacts. Simple!
> >Alas, hard to reproduce the cards automatically. Easy with a hand
> >punch though.

xerog the cards with black paper behind them.
Let people who want them punch their own holes where the copy has a spot.