Julian put together a plan for a RFID zapper, the information below was translated but reads not bad.
UPDATE: Julian was kind enough to send in a hand translated version. The text below has been changed accordingly. (Thanks Julian)
“This drawing represents schematically the circuit board of a disposable camera with built-in flash. Also, the necessary design changes are illustrated. Essentially, the “on-switch” (On-Schalter) must remain closed permanently, e.g. by a solder point. The switch for activating the flash (Blitz-Schalter) must be deacitvated and/or removed, as well as the flash bulb (Blitz-Birne). Now a coil with 5 windings of 1mm diameter enameled copper wire (Kupferspule) is connected to the capacitator (Kondensator) with two cables and a momentary switch (ZAP-Schalter). The little bulb (Bereit-Birne) that glows when the capacitator is fully charged can stay in place. But it is better to remove it and connect it with two extension cables again. So, it can be glued clearly visible under a hole in the case afterwards. Finally, the battery holder (Kontaktklemmen) gets removed and a recharchable battery (Akku) is connected to the contacts with cables and a switch (ON-Schalter). For convenience, a charging jack (Ladebuchse) can be added as well. I used a 3.5mm audio jack.
The contacts of the momentary switch used to discharge the capacitator into the coil can weld together due to the very high current. This problem disappeared after 6 or so activations.
An interesting observation can be made when activating the Zapper about 0.5” away from the metal lampshade of a anglepoise lamp. It produces a “ping” sound as if one flips the fingernail against it. This phenomenon indicates that the magnetic field of the Zapper should be sufficient to destroy any RFID- chip at close range.”