RFID (Radio Frequency Identification) readers are quite common today. They are the method of choice for controlling access in office blocks and for entry systems for public transport. Small RFID tags are injected into animals for identification if they get lost. Vehicles have tags on them for toll collection. They are even used in hospitals to tag disposable equipment in operating rooms to ensure that no foreign objects are left inside patients. The cost of the technology has come down drastically over the years to the point where readers can now be purchased for less than $10. They are easy to connect to an Arduino and easy to use. As a result, all kinds of cool projects can be created out of them.