Audioquest Eagle Eye Digital Cable - how to use

Thanks could not find any info on it at all.

Like all AQ DBS cables the Eagle Eye has a battery pack with a set of (often obscure and hard to source) batteries that should be left connected at all times. As @mental notes the button is for periodic battery life testing. Frankly if you leave the batteries until the green light no longer comes on they are well past usable -- in real world use replacing the batteries at least once every five years will deliver a clear improvement in sound. As the Eagle Eye is a long obsolete cable I'd guess that the batteries are due for replacement. However you should also be aware that if disconnected (i.e. if the small plug into the battery pack is pulled out, or for that matter if you change the batteries) it will take 48-72 hours for the DBS field to fully reform and performance will improve over this period. Net net ask your dealer if she changed the batteries recently, and if not look into buying a new set