2011, Lisa Unger, Darkness, My Old Friend, Broadway, published 2011, →ISBN, page 57:
The toddler at the far table issued a little shriek of delight over something. "Indoor voice," his mother whispered.
2014, Bobbi Govanus, How To Pilot When We Were Raised to BE Stewardesses: Reinventing Your Life with Passion and Purpose, Lulu.com, published 2014, →ISBN, page 18:
She knew when I was on a business call that she had to be quiet and use her indoor voice.
2014, Kate Racculia, Bellweather Rhapsody, Houghton Mifflin Harcourt, published 2014, →ISBN, page 242:
She's easy to be with, provided you don't mind the constant chatter, the non-sequitur song cues, or her total lack of an indoor voice.