How do you change the battery in the remote key chain?

Ford sold a Ford branded alarm through the parts department. These sometimes were a dealer installed option on new cars. Mine would randomly stop responding to the remote and I would have the same symptoms as you describe. I had it removed and the original equipment factory system still worked. Be warned, if you have the Ford "accessory" alarm, your key fobs (remotes) are different and the method to program them is different from what you will read online. You can tell if you have the system by looking at your key fob. The standard Mustang key fob is a 4 button (lock, unlock, panic, and trunk). The accessory alarm uses a 3 button remote and clicking unlock twice would pop the trunk. I really wish I had a picture of the remote because there are 3 button Ford key fobs for cars without a trunk release although I don't think you should have one on a Mustang. Long story short, if you have the accessory alarm, you can solve your problem by having it removed but you will need new 4 button key fobs to remotely lock/unlock your doors

Do any of the other buttons on the remote work, like the horn or trunk-open buttons? If they do, then you might have a blown fuse or relay switch for the specific problem. On my Grand Am, there are relays for "Door Lock", "Door Unlock" and "Driver Door Unlock".

Have you replaced the battery lately? If so , you could have a bad battery in your key. It is a small microchip in some cares and will effect unlocking and starting the car if the battery is weak or dead.

check the battery in the keychain. or replace. Make sure the keychain remote doesnt get wet!

Here are the options for disarming a factory alarm while it's going off:

1. Close all doors, trunk and hood. Alarm will stop after preset time.

2. Hit the unlock or lock button on the remote. (One of the 2 works... I just don't remember which.)

3. With all doors, trunk and hood close, insert the key in the driver's door and unlock/lock the doors manually.

Also, is it a factory security system? Is it a honda key fob? or a remote start system perhaps?

Are you using the the keychain to lock unlock the vehicle? A low battery in the keychain will send wacky codes to your vehicle alarm system and will not set properly. Try using the key in the door to lock unlock vehicle. IF the alrm does not go off when using the key in the door, then you probably have to change the battery in the key chain. Best guess without being there to look at vheicle.

Assuming the car battery is ok (if not, buy a male to male cigarette lighter at the auto store and connect to another car until charged enough to unlock the doors...but don't try to crank the ignition!). The trunks won't open if the battery went dead with the alarm set because arming the alarm physically locks the releases.

Sounds like the key code is switched off because you replaced the key fob battery. Try unlocking the car manual with the key in the door lock. Then switch the ignition on to reactive the keyless entry. If this does not work, you might also try pressing the fob unlock button with the key in the door lock until the dash led flashes.

At first look, I would have guessed that your battery in the door opener was dead, but that is not the case. I suggest driving to a nearby Chevy dealer and ask one of the salesman if he/she can help. They have always been helpful to me. If not try another one as they are in business to sell not only cars, but service also. They will be your best bet to fixing it. :D

Is this a factory installed alarm system? If so, unlocking the driver door with the key will allow the car to start. If not then you will have to remove the aftermarket alarm system to start the car.
If you have a factory alarm system you can get a new FOB (key chain alarm button) from a ford dealer, but it must be programmed using a scanner , before it will work in your vehicle.

the key fob remotes need to be reprogramed or have the battery checked... make sure to have all key fob remotes present when reprogramming...