Hmmm... I've heard that one before. Not to say anything bad, I'm sure your uncle actually did tell you that. But it ranks right up there with how anyone can look through your windshield, copy down your VIN number from the little tag, go to the dealer and tell the secretary there that you lost your key FOB, show them YOUR own ID, and they will order you a new key FOB for "your" car...then you don't need to break a window or use a slim-jim to steal a car. I think both stories are on the "urban myths" website...
Yet, it does make sense to get your own alarm system if you feel that strongly about it. For me, my car is parked in a parking garage all day at work so if anyone sets off the alarm I won't know about it anyway...and with new alloy wheels those locking lug nuts made sense too.