The General Authority of Islamic Affairs and Endowments of the United Arab Emirates has officially issued a fatwa against vuvuzelas. The declaration of Islamic law declares the noisy plastic trumpets to be haraam, or forbidden by Islam, when they reach above 100 decibels.

The UAE is apparently concerned that the instrument, which has dominated all matches at the World Cup, could become such a disturbance in the Islamic state that would even disrupt daily prayers. The National's Eugene Harnan reports:

According to fatwa number 11625, the horns can be used only in stadiums if they pose no harm. "However," the ruling declares, "importers and traders ... must ensure that its power is not over 100 decibels so as to avoid damaging people's hearing."

The authority based its decision on a study that found human hearing could be damaged if exposed to more than 100 decibels. ... The National's own specimen vuvuzela easily maxed out a sound level meter, which can record up to 126 decibels. Even the quieter horns, rushed out after the first wave of complaints, are only 20 decibels less noisy - still over the limit.
The UAE is in good company. The Wimbledon tennis tournament in Great Britan issued a similar, if non-Islamic, ruling.