I have seen these Kee-Blok doorknob covers several times. I even own one of them. I am trying to determine what type of pick would be used to pick them. Would it be a double sided wafer pick? Here is a picture of this type of lock:
http://www.locksmithtoolandsupply.com/store/merchant.mv?Screen=PROD&Store_Code=PLT&Product_Code=527-0010&Category_Code=MLD
The keys to these are quite small and short... they are designed to go around a doorknob to prevent you from accessing the keyhole.