For those who use Apple's wireless mouse or keyboard, you might find the appearance of a flashing Bluetooth menu bar item bothersome when the batteries in your device run low. Disabling the item from the menu bar by command-clicking and dragging is only a temporary solution, as it will continuously reappear until you have recharged or replaced your batteries.
Since there is no option to prevent this warning from appearing, the following hint may be useful for those who do not use and will never need the Bluetooth menu bar item: Simply move or rename the Bluetooth.menu file from the /System » Library » CoreServices » MenuExtras folder.
[robg adds: In general, I do not advocate moving or renaming system files. However, as a user of both the wireless mouse and keyboard, the flashing warning is annoying -- as is the fact that it will automatically add itself back to the menu bar even if you remove it. If you try this hint, I strongly suggest putting the menu extra back before running any Apple Software Updates. If anyone has a better solution, please post it in the comments.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20071211113234340