The Spouse Alert is a silver Christmas bell. It is found on the seventh sublevel of Frontier Cavern. To retrieve it simply carry it back to the ship.
Notes
Olimar's Journal
"Sometimes I miss my carefree bachelor days. Once you have a family, those days are history! I like spending time with my wife, but sometimes I just want to be alone."
Sales Pitch
"Put this on your spouse and you will always know if he or she is approaching. How convenient! A must-have item for couples who like to hide things."