Signal watch

The signal watch is a special wristwatch owned by Jimm Olsen, who uses it to call on Superman whenever he is in danger.

Physical appearance
There is a light gray button where the hands would be, and a blue strap.

Powers and abilities
The watch is tuned to a frequency that only Superman can hear.

Scooby-Doo! Team-Up
When Caeser's Ghost appeared in the Daily Planet, Jimmy pressed the button, which went out to Superman while he was battling Grax, Mongul, Terra-Man, Nova, and Brainiac out in space.

Later, when Superman had been transformed into Super-Monster by red kryptonite, he thought about his watch, but it wouldn't work when Superman was the monster, himself.

Appearances

 * Scooby-Doo! Team-Up (DC Comics)
 * #6. Truth, Justice, and Scooby Snacks