cursebreaker

My Uncle plans to install CCTV at his home, and he's asking me to help him figure it out. I think I've got most of the stuff down, (with the accessories and all), but I can't figure out what to use with the audio. He's using CAT5 so I used a video balun for the cameras, but what to do for the mike? My Uncle inquired in the place where he bought the DVR and he says, they said something about RCA?? (I wasn't there). He can't explain it to me that well. Helppp....???