Beeping from dash

Ok ,my Red 2005 just started making this beep from some where inside the dash ,i kind of think it is inside the AC vent ,i had this car almost completely apart and there is nothing there that could make this sound . A few think it is a tracker but i dont know when it could have been placed there unless it was at the Ford garage ,tire shop or smog shop .
It stopped about an hour ago ,but it would sound with everything turned off and key out of the car https://m.facebook.com/story.php?st...Zj3LQ5xkul&id=100011163619813&mibextid=2JQ9oc

Looking up on line ,some trackers will beep when batteries are running low so hopefully this thing died because it stopped beeping .
Must have been there a long time ,i have had it for two years now ,i am betting the kid i got it froms dad put it there to keep tabs on him