I have used ultrasonic insect repellant devices in the house, attic,
basement and garage with very good results.  Most just plug into any
household outlet and make no more than an occasional ticking sound.

Specific to pianos, I still use the old-fashioned packets of whole
cloves and bay leaves in cloth bags.  I have no idea how effective
this is but the smell is nice.  I also use paradiclorobenzene also
in cloth bags inside the piano.  I have never seen any sign of insect
or otherwise inside the pianos.  Whether it is one thing or the group,
I do not know. We have no problems with spiders or any other insects
in our home.

Mark Reinhart
Charles Town, West Virginia