This musical instrument will radiate magic if detected for. It appears as a normal horn, or possibly any one of the many magical ones. 

It will sound a note and call forth a mass of bubbles which completely surround and blind the individual who blew the horn for 2-20 rounds, but these bubbles will only appear in the presence of a creature actively seeking to slay the character who winded the horn, so their appearance might be delayed for a very short or extremely lengthy period.