I was trying to work out what you would back up, but I realised you mean to reverse.
Simplest trick if you are parking in the same garage is to put down a brick where you want to stop.
There are also bumper sensors that can be added, but I don’t know what the cost difference would be.
Anyway, I think a motoroing forum will be a better place to ask.
Actually I’m looking for one of these systems as a gift for my husband, Erik (I don’t drive) for parking in public places as well as backing out from them in difficult areas. So the brick idea, while nice for parking always in specific garages is a good one, it wouldn’t work when parallel parking etc.
Becoming a member in a motoring forum for just this single quest seems to be going over the line a little since I’ve known these members here for a number of years and have received very good advice here. I have also read numerous reviews from Amazon and a few other sites who sell these systems. Lots of the reviews are from folks who have no qualms about rewiring their electrical systems for hard-wired systems, and there is little given about the wireless ones. They are not cheap and I don’t feel I should invest in any carelessly (I don’t have those kinds of funds).