Rear view Cameras and Reversing sensors.
Rear view cameras are a great aid, not only for reversing but also for keeping an eye on a tow vehicle or seing behind if you have no rear window.
Monitors are available as dash mounted or clipped onto your rear view mirror.
If you just want to know that you are not about to hit anything when reversing, then reverse sensors are thing.
These ones have visible notification as well as audible.