Authorities may have all prisoners to wear the Happiness Hat a few hours during the day. The Happiness Hat invented by Lauren McCarthy forces you to smile. It you don't smile, It detects whether or not you're smiling. If you aren't, it jabs you in the back of the head with a metal spike.
If prisoners keep smiling, smiling becomes their second nature. If smiling becomes their second nature they become kinder, less violent and commit less crime.
More info about the Happiness Hat is here and in the video below.