All you need is a phone line! All phone lines have a constant flow of voltage, around 40-70 volts (up to 100 volts when it rings!), but you can't just plug stuff into it and expect it to work.
Children older than 5 and more than 40 pounds must ride in a booster seat until the child is 8 years old or is taller than 4 feet 9 inches. Anyone over the age of 8 must be protected by a safety belt.
Depending on the model, boosters fit children from 30-40 lbs. up to 80-125 lbs. Some manufacturers require a minimum age of 3 or 4. The driver or parent may be cited for misuse if the child is under the minimum age or weight specified on the label or if a booster is used with just a lap belt.