The remote entry system employed on newer Fords allows you to lock and unlock the doors from around 30 feet away. There's also a "panic" button that sounds a rapid alarm. And on those Fords with a liftgate, you can unlatch the liftgate window from the remote as well. Occasionally you may need to reprogram the Ford remote key fob. The vehicle referenced here is a 2010 Ford Explorer, but the process is much the same for other Ford models.
Open the driver's door of the Ford, press "Unlock" on the armrest panel and place your key in the ignition.
Turn your key eight times from "Off" to the "On/Run" position (the position just before "Start"). Do this within 10 seconds. You should end at "On."
Press any button on the key fob. You have 20 seconds, so don't dawdle.
Press any button on the second key fob you wish to program, if any. Again you have 20 seconds to do this. You must reprogram all the key fobs for this vehicle at this time; otherwise they will no longer work.
Turn the key in the ignition to "Off". Test your key fobs for correct operation.
If you wait too long to press the buttons, you must start the process again. For specific Ford instructions for your vehicle, refer to the owner's manual.