Car Seat Belt Safe Lock, MuStone Car Safety Seat Strap Belt Lock Tite Tight Harness Clip Safe Buckle for Baby (Black) is available in Car Seat Protectors

You have to remove the strap from the baby seat, thread the belt through this then refit to the seat. Takes around 5-10 minutes.
This Item needs to unhook your car seat belt to thread them through this buckle. If seat belt can not unhook, this is NOT suitable. 
Car safety seat strap belt clip buckle helps to locate and curved seat strap to ensure the safety of the baby.
Easy to fit but stops the child unfastening the straps and climbing out of the seat.
Easy to clip shut and open.
Material: Plastic 
Color: Black
Size: Approx. 14.5 * 4cm / 5.7"*1.5"
Quantity: 1 piece

Package:
1 x Car Baby Safety Seat Strap Belt