If you have a new-born or young child then you will be all too familiar with the rear facing car seats, that although are safe, make it very difficult for you to be able to see the child. You may want to check if they are asleep or even just check that they are ok on a journey and without a separate mirror this is virtually impossible.
You can buy a mirror that either sticks on to the window or wraps around the rear headrest. You then can line it up with your rear view mirror in the front to allow you to see the baby’s reflection at all times.
From my experience, the suction mirrors are not as good as they often fall off and mine even fell off on to my child waking her up. Prices vary from a few pounds up to about £10 depending on what style you want and there are some great child friendly designs available meaning that once your child is old enough to front face, they can play with it.