These were an Austin Electronics offering first. They had a version with two independent 360 strobes and a version with two remote 360 strobes with a power supply in the middle, the literature didn't necessarily specify; kind of like some versions of the responder. The version with four corner strobes from whatever edge bar was being sold at the time was always more expensive. I have owned a few different versions and the 360 beacon guts very a bit from year to year. These are a cool item because Austin electronics always seem to have a slightly different and/or cheaper version of stuff, these are a great example. I have had and sold a few of these and wish I'd hung on to one.