Slavery: A series of erotic games (book 04)
"Do you want to tell her, Julia?"
"It's not malfunctioning, Marcia. It's called a Slave Trainer. Its designed function is to bring a slave to the cusp of orgasm, then shut itself off when it detects one is going to start. You can't have a climax in one unless you bring one on yourself, which is prohibited."
Marcia got this horrified expression on her face. "Fuck, no!" Marcia exclaimed.
"I'm afraid so," I said. "But I'll let you have an orgasm as soon as you beg to be fucked."