Wearable Audible Alarm

We are developing a game and seek someone to design and develop a small wearable device that triggers an audible alarm once the item it is attached to is removed. The item is a baseball cap. Person will attach the wearable device to the adjustable strap at the back of the baseball cap. When the baseball cap falls off the person's head while playing the game, the alarm goes off, between 60-80 decibels selected by user. The device would need to be able to sensor that the baseball cap has fallen off, and have enough power for at least a 12 hour period. The device cannot emit harmful energy as it will be near the users head.