Miniature audio transmitter

From Chuck Wiki

Miniature audio transmitters are often used by John Casey and Sarah Walker to listen in to what is happening to Chuck. They can be concealed in many things. Some notable ones include:

• A picture frame (from Chuck vs. the Sandworm)
• A tie pin shaped like a guitar (from Chuck vs. the Imported Hard Salami)
• A watch (from Chuck vs. the Imported Hard Salami)