Tech and Signals

Across

1. Chemical used to make plastic foam

3. Send a message electronically

5. Not clearly determined or specified

8. Device detecting objects using radio waves

10. Hidden storage for valuables or data

12. Device for wireless audio transmission

13. Negative electrode in an electrical device

Down

2. Device for receiving radio signals

4. Sound made by a sonar signal

6. Device that sends out signals

7. Large scale or overall perspective

9. Chamber between two pressure environments

11. Page bottom section in a document