Some vehicles have the option to purchase a built-in child restraint system. The child car seat is built into the vehicle seat and will unfolds from the vehicle seat, revealing the harness system. The child is secured into the built-in car seat in the same way as a regular child car seat. No tether strap is required as the straint is an integral part of the vehicle already. In order to use these systems, your child must have graduated from stage one - (must be over one year old and 9kgs/20lbs).
Please note that these intergated systems general do not accomodate your child as long as a regular car seat would (may only be able to use up to 36lbs), check your vehicle manual to obtain this information. Also, if this system breaks you will not be able to get it repaired., just like a regular car seat.