the ID20 have the biggest antena of his rfid class..the bad part is that the range is not so big.You can buy the ID-02 that have no antena and buil one yourself,getting longer range,but that depend of your electronic skill.Wireing is easy 2 digital pins,5v and Gnd(careful with soldering the pins,the aligniment of pins doesn't fit on the usualy breadboard).The identificacion rfid tag comes in button,card,glass capsule..the bigger it is,the larger is the range.It is a great project,but it's not fit for me...since is quite easy to hack it
..anyway check out:
http://www.instructables.com/id/Arduino-RFID-Door-Lock/