Well where I live (and in other U.S states as well) they have the exactly same authority as a private citizen which is basically nothing. They can make a citizens arrest and/or have basic self defense and good samaritan rights. Licensed private investigators have more authority even. Sure some of them carry guns but so do half the law abiding citizens in this and 36 (at my last count) other states and we don't go around exerting some special type of authority as a result.