From the department of things you never knew you needed, and were probably right:
I don’t think you need me to explain what you do with them, nor that it probably doesn’t matter that you wouldn’t be able to see them under a blouse or a shirt.
I’m just afraid that when I see someone with a flashing red belly button, I’ll thoughtlessly mistake them for a walking answerphone.
I think the manufacturers have missed a trick. If you could switch the belly lights on and off by pressing them, it could provide an endlessly interesting way of making new friends.