What is the law and fine for wearing seatbelts?

Ten ($10) dollars for driver and adult passengers. Adult includes everyone from age eight and older. A citation for anyone under age 16 is given to the driver of the vehicle.
Seat belt law
Any automobile sold in the state of Wisconsin must be equipped with safety belts.
All drivers of motor vehicles and all passengers over the age of four must wear safety belts.
These laws apply to Wisconsin residents and non-residents alike in all front seat positions and in rear seat positions with three-point belts. Children under four are required to be restrained in an appropriate child safety restraint (see Child safety seats).
Currently, Wisconsin has what is known as a secondary enforcement seat belt law. It allows law enforcement to ticket a driver for not belting up only after the person has already been stopped for some other violation.
A standard, or primary enforcement seat belt law would allow police to stop and ticket a driver for not wearing a seat belt, just like any other routine traffic violation.
Where a primary enforcement law exists, seat belt usage is higher. States such as California and North Carolina have realized a significant increase in safety belt usage (to 80 % in North Carolina) through the combination of a primary law and an aggressive awareness and enforcement effort.
Wisconsin law provides for a fine of $10 and no points are assigned against a person's driver record. Those subject to the penalty include drivers, drivers with unrestrained passengers 4 to 16 years old and passengers at least 16 years old.
The penalty for violating the child passenger law involving a child under the age of 4 is not less than $30 or more than $75. The penalty for violating the child passenger law involving a child between the ages of 4-8 is not less than $10 or more than $25.