Teens in The Sims 2 can choose to sneak out after curfew without permission. This action is available on the phone from 10:00 PM to 1:00 AM. To have a Sim sneak out, click on a phone and choose "Call...Sim....Sneak Out", then the Sim will be asked with which teen they would like to go and if accepted a message will appear on the upper-right corner with the selected teen Sim saying "Cool! I'll pick you up at 1 AM." If rejected a card will pop up saying "(Sim Name) doesn't feel like going out right now."
When the car arrives, the Sim will tip-toe to the car and will be out from 1AM until 4AM.
If the Sim is seen, an adult Sim will run to the teen and lecture her/him, telling her/him to go to bed. The car will leave, and the teen is forced to go to bed or be "chastised." When a Sim refuses to go to bed, they will be followed until they receive a slap in the face. Teens can also be caught by the police when they're out of the house, who will promptly send them home in the back seat of a squad car.
Teens that successfully sneak out get a positive memory of it, while teens who are either caught sneaking out of the house or caught by the police will get a negative memory of it.
It's a good idea to have all other Sims sleep in a different room than the sneaking teen is in. If Open for Business is installed, the door to that room can be locked, increasing the chances of the teen successfully making it to the car.