Actually, I believe they meant "clicker" as in the one pictured below:
http://www.petsmart.com/media/ps/ima...2235_12d33.jpg
Not to be confused w/ a radio transmitter, such as this one:
http://www.petsmart.com/media/ps/ima...7429_39d81.jpg
I just purchased a clicker this past weekend. My yorkie comes running to the noise. Haven't started training him yet, but I enjoy the fact that he runs to the noise anywhere in the house.