The Metal Detector is an item in Wimpy Boardwalk. Your Poptropican needs this item to find tokens on the beach.
When you roam the Metal Detector across the sand, the red light in the middle needs to be blinking green, once the green light stops blinking and stays green, click with your mouse and you will get a token. You will need this item to find tokens and the Car Keys.
The lady on the beach will tell you to watch it if you try to put the metal detector on her while she's on the beach.