Just use the key.
I have an odd problem in my GP. As the title says my keyless entry stopped working. We took the fob to the dealer thinking it was a battery. They said the fob was fine so it is the car. What part of the car gets those signals? I thought it was just the antenna or something. Would replacing that part be expensive?
There would be a receiver somewhere in the car. If you knew what/where to look you could go to a pick and pull yard if they have any in your area.
Not sure how GM keys these things - certain radio frequency, might have to program the receiver to the key. There are millions of cars with these things out there, but only one set of keys works with one receiver (you don't see other GP's un-locking when you hit your button). But I would imagine the re-program is fairly simple... like a garage door transmitter. Something made as a matching pair would be very difficult to handle logistically. When I had my Audi the only thing you had to do to re-program a key was hit the lock button, then lock with the key, then press the lock button again. Or something to that extent. Might be similar with a GM?
I'd ask the dealer what would be involved, and then look into your options. Also, it could just be a corroded connector on the receiver, or a faulty relay from one of the outputs (does the central locking still work from the interior switch)... could be any number of things on a 12 year old car. Seems like something you'd need a full GM scanner to track down (to see if the receiver is taking commands). If the receiver works, but the car isn't sending an unlock command to the door locks, it could be the output, a relay, the solenoid, or wiring in the middle. If its plain and simple the receiver - check for faulty wiring, then replace the part if it is the part itself.
That being said... if it's more then you want to spend right now, there's always the key. If the central locking still works (and you don't have to push the button down/up for each door) I could live with no transmitter if it were me. Having to do each door manually does suck (I had a Mk2 Golf with manual locks... it wasn't fun, but you deal with it) and I'd fix the central locking.
Close all the vehicle doors.
Insert the ignition key into the ignition lock cylinder.
Press and hold the DOOR unlock switch.
While holding the DOOR lock switch in the unlock position, cycle the ignition ON, OFF, ON, OFF.
Release the DOOR unlock switch. The doors will lock and unlock to confirm the program mode.
Press and hold the LOCK button and the UNLOCK button simultaneously on one keyless remote. After a delay of approximately 15 seconds , the doors will lock and unlock to confirm the programming of that transmitter.
Other than that I'm of no assistance.
Happened on my dad's 2009 avalanche. he figured it was the battery in the fob, but after changing it the problem persisted. he called the dealership who told him it was some kind of mess up in the receiver in the truck. their advice was to disconnect the battery for half an hour, the re-connect. after doing that the keyless works again.