It is a light olive-green colored device with a light tan button, a red dial, and a light gray antennae that are used to track sponges within a mile radius.
Role in episode
Sandy invents the tracker after SpongeBob goes to New Kelp City. The device is soon destroyed by Squidward as he didn't want the Bikini Bottomites searching for SpongeBob to find him. It should also be noted that Squidward purposely destroyed the device with a hammer, but claimed that he dropped it, when it was obvious he didn't.