What does the idiom pick up your ears mean?

The idiom "pick up your ears" is not a commonly used phrase. It's possible you may be thinking of a similar phrase like "prick up your ears".

"Prick up your ears" means to become alert and attentive. It suggests that someone is paying close attention to something that has caught their interest.

Example:

"The dog pricked up his ears when he heard the doorbell ring."

The phrase highlights the physical action of a dog raising its ears when it senses something important, and this action is transferred to mean being alert or attentive in humans.