This is the most versatile safe device that you need for any pet travelling in the car with you. In the example of guinea pigs, you can connect their carry cage direct to a seat belt holder which will ensure the cage is not going to fall off at any time. You can also use this device to transport any other pets like cats/ dogs that wear a harness. This will keep them safe in their own seat, stable and locked in so that they are safe in the event of stopping.
This is something I use all the time here in Australia and have a number of them for different applications.
They come in 3 different colour options – Red, Black and Blue.