I just bought a used 2003 Explorer and have had this happen 3 times now. The first time I was parked and loading the vehicle with the key in the ON position, engine off, my window down, back gate open, with my headlamps on. This was about ten minutes. When I went to leave, my headlamps blinked quickly as I turned the key, the red light on the dash for the alarm blinked quickly, and when I tried to start it, it clicked and would not start. I waited a bit and tried again. No start. I read my Ford book while waiting for road service. I read about the PATS system, and since then have also seen some people thinking the alarm system is running down their battery while sitting and searching for the key to start it. I'm not sure, but when the man got there he hooked up the battery to charge and it did the same thing at first. I got out of the car, hit the lock button twice and it beeped twice instead of once. I hit the unlock button once, got in, tried to start, click click click. I took the key out and turned it upside down and it started. Ran fine after that for days. Now it has done it again. Did same thing with jumping with battery, etc. it does nothing, like the battery is totally dead, but it is not that old. Any help on what this is and how to fix it?