What kind of a scam is this ?

i just got a call, saying i one a security system by sighning something at the fair grounds in the last six months, maybe i was at a home show or some thing i dont remember, it is valued at 1200 dollars not including the install fee, so were looking at 1200 dollar, is this a scam ? the lady on the phone said that every thing was free except the monetering fee ???? but see i would be happy just to sale the equipment cheap to some one that really wants a system, i dont remember sighning anything. if i really did when some thing how can i come out ahead on this deal ? a representative is sapose to come to my house this week to take to me about the installation, how can companys use this sale tecniec to try to make money ? if thats what they are trying to do ? or maybe i really did when ?