In them, you will notice that it says they have switches available for installation on vehicles without backup lights, but then it says, it is ~not intended for use as a backup alarm.  The models this manufacturer provides for backup alarms are the 102dB units.  I suspect it is an osha threshold that was established for noisy construction sites and for people walking around wearing hearing protection.  I use these on my commercial vehicles and skidsteer used on landscape projects so that I don't annoy the HELL out of the entire world when I am backing up.  It is a way of announcing to the people near you that you are backing up, as opposed to everyone in the 3 block radius.  As for technical legal requirements, I have not had any issues, at all, but you need to decide that for yourself.  These are what I prefer and don't get "accidentally disconnected" because they are so annoying.  

This listing is for what is shown, NEW in Original Package.  I have included a Best Offer tab for those who would like to save money and do not care about packaging.  I have a BUNCH of these, ALL NEW, in various condition.  Some have no papers and no box, some have boxes that have a little water exposure (they are weatherproof alarms,) but the rest are as shown in the photos.  All buyers get a NEW alarm.  

I will likely accept all reasonable offers and ship you A BRAND NEW alarm relative to your offer.  LOW offers will get a NEW alarm without packaging or papers, and maybe a little dust.  Buy it now, will get ones as shown in photos, with box and instructions.  :o)