welp. i had this issue with my '08 avenger and found this site while searching for a solution. here's my story:
a few months ago, i was leaving my office and hit unlock on my fob, walked to my car, and went to open the door to no avail. i had to use the key manually, setting off the alarm, and then the fob would work. so everytime i went to my car, i had a one horn honk, hit unlock, and into the car i went. very annoying. earlier this week, i read in this forum that some things can throw off the signal. i thought "what the hell do i have that could do this?" i then remembered that i had my phone charger plugged in at all times in the middle bucket storage... or whatever it's called, for the last few months since i bought it.
in any event, i simply unplugged it and success. since then i have had no problems. so maybe if you have something plugged into the cigarette lighter, or maybe just any type of cable, for too long or when the car is not running, unplugging it when the car is not in use might fix it.
i hope this helps out! i know this is such a huge annoyance.
good luck everyone!
edit: side note - i had to go to my dealer for an non related issue, i brought this up and they said the standard "we can run some programs, but it's probably your fob." i have 2 fobs and they both did not work. mine are not after-market or anything, they came with the car. so i do not know if this works for after-marketing fob's.
Last edited by shutdown; 05-14-2010 at 12:15 AM.