I think you have to leave the key fob in the truck. I did the same thing with my dog(when it was much cooler) - rolled windows down some then locked it and horn went off about 50' from the car from him moving around.My current F250 has idiot sensors it it.
I have two g’son who are 13. I tried leaving the truck running while I ran into a quick stop to grab them some Poweraids after a wrestling tournament. They barely moved and my dang horn started going off.