Peace Maker by Malorie Blackman

Michela knows the law - everyone must wear a Peace Maker device at all times, and it must never be tampered with. Non-aggression is her society's founding principle, and the Peace Maker the means by which is it enforced. But Michela is desperate to experience the full range of human emotions in her own fantasy world of books and games, and the Peace Maker is the only thing stopping her.

And when her mother captains their ship into enemy airspace and they come under attack, it seems that Michela's freedom from the Peace Maker may be the only thing that can save them. Particularly suitable for struggling, reluctant and dyslexic readers aged 8+