Stupid music question
 

Why do bands playing live wear what looks like hearing aids?

They are in-ear monitors. This is an alternative to the wedge or standup monitors some bands use. It helps the musicians to all hear each other and stay together. The sound tech can mix these differently so if the drummer wants more bass he can have it, while the singer may want more background vocals so they can harmonize, for example.

Up on stage without monitors is tough.

And the in-ear ones probably block a lot of the distracting outside noise out. Like in-ear headphones (etymotic, shure, etc.).

There are no stupid music questions, only stupid music.

Thanks, I it was something like that!