While this arm wrapping appears to be some sort of beneficial device, it actually draws the attention of supernatural creatures of exactly the opposite alignment of the cleric wearing it.

This results in the cleric being plagued by powerful and hostile creatures whenever he or she is in an area where such creatures are or can appear.

If the cleric is of 10th or higher level, the attention of his or her deity's most powerful enemy will be drawn, so as to cause this being to interfere directly. 

For example, a Lawful Good cleric attracts various demons and eventually the notice of Orcus or Demogorgon. 

Once donned, a phylactery of monstrous attention cannot be removed without an exorcism spell and then a quest must be performed to re-establish the cleric in his or her alignment.