An awesome little card, with a tiny little problem
For RFID Field Detector
This little card is SUPER cool. Haven't had it for long but it was fun seeing the little LED blink for everything that I put it near that had RFID.
Word of warning though - LED1 is green, not yellow. If it glows yellow (like it did for me), it's too late and you won't be able to use that LED again. I learned this the hard way by trying to see what kind of RFID field my magsafe charger uses (LF by the way, just save your card and don't test it).
I don't think that's something worth penalizing a star for, just something to keep in mind.