KEY WILL NOT UNLOCK DOOR AFTER INSTALLING NEW BATTERY

thats how its suppose to work the key resets alarm ==by a fob online for a few dollars and program to car [free program] ==when you use key to unlock and enter vehicle you have a few seconds after opening door to turn vehicle on or start it and doing so resets alarm when you leave vehicle and lock it alarm is active

Replace battery very expensive to get new one they are button batterys get hi power ones

unlock with key and hold key over for 30 secs(windows may go down)then lock with key and hold over for 30 secs(windows may go up)then press remote unlock button and hold for 30 secs,you have just reset system...the closer you have to get to the car for the remote to work the lower the battery power.sensor on top of dash(little black dimple)rarely,if at all, goes wrong.....

You lost your program of the key module follow these instructions.

To Program a Remote for a VW
Put your good key in the ignition and turn to "ON", do not start the engine. Make sure all the remotes you want to use are present because they have to be programmed at the same time.
- Close the door and insert key #2 into the driver's side lock. Lock the door.
-Within 5 seconds of locking the door, press unlock 2 times on the new remote, key #2.
-(if this is remote #3, press unlock 3 times. if this is remote #4, press unlock 4 times).
-If there's a chirp or beep do not press it again. This means that the car has recognized the new keyless entry remote.
- Repeat with other remote or unlock the car and turn off - done.

The remote likely needs to be reprogramed. If you have both remotes you will need to take these to the dealer and have them reprogramed.

On some cars/trucks/SUV's, the alarm will go off if the car is unlocked with the key or if the door is opened (even from inside the car with the alarm set). Unlocking with a key does not always turn off a car alarm. Best advice, go to the dealership to get a new key-less entry remote, or get a new alarm installed with a remote to override the original alarm system.

usually after opening the door you can deactivate the alarm by pushing th unlock button or simply insert keyy in ignition and turn it on.

try changing the drivers door lock

It is entirely possible that the unlock button on the remote is worn such that it is not making contact. I've seen this happen many times, as the unlock button is pressed so much more than lock. You might try to reprogram the remote first before you look into getting a new remote. The procedure goes like this. Close and lock all doors Key in and out of the ignition 6 times, hazard lights should flash twice Turn key into accessory or on position Unlock and lock doors with drivers switch Press lock or unlock on remote Hazards should flash again to verify recognition turn key off  manually unlock door and then open and shut it.  you should then be able to test remote. 
The key to the procedure is doing step two quickly Hope this helps, if not you may need another remote or see dealer.