Horn
Yep it is a requirement on my RV's along with smoke. Had this one since 2011 and folks love it, me too!
Wolo Bad Boy Air Horn. I had so many folks come up and ask me about it at OSH. It is useful, fun, helps with safety and gets your wingman's attention if they forgot the freq or to pull their chock, etc. Once you have one you will wonder why it is not a requirement! Have fun!