Many sellers offer keyless entry remotes without programming instructions.  I purchased one after searching the net for the instructions.  These instructions worked for me.  Hope they work for you too.  I have a 2005 Scion XB.  I understand that these instructions don't work for 2006 models unless the dealer has installed the keyless entry in the car.  If you have a 2006, please check to make sure that the keyless system is activated and installed before you buy.  Good luck!

There are four different modes you can use to program remote door lock functions.

Confirmation mode allows you to check the number of transmitters recorded.
Add mode allows you to add a transmitter without disturbing existing transmitters.
Rewrite mode allows you to replace all existing transmitters with new ones.
Prohibition mode erases all transmitters and turns off the remote door lock function.

Confirmation mode. To check for the number of remotes programmed into the car:

Start with the key out of the car, driver's door open and unlocked.

1.Insert key in ignition and pull out
2. Within 5 seconds, insert the key in the ignition and pull out again.
3. Within 40 seconds, close and open the driver's door twice, then insert and remove the key from the ignition again.
4. Within 40 more seconds, close and open the driver's door twice, then insert the key in the ignition and close the driver's door.
5. Turn ignition switch from LOCK to ON to OFF three times, leaving the key on for one second and off for one second each time.
6. Remove the key from the ignition lock.

The doors will lock and unlock themselves at about 2 second intervals. The number of times that the doors lock is the number of remotes that are programmed into the car. If the car locks/unlocks 5 times, there are no codes registered.

Add mode. To add a remote without disturbing existing remotes:

Start with the key out of the car, driver's door open and unlocked.

1.Insert key in ignition and pull out
2. Within 5 seconds, insert the key in the ignition and pull out again.
3. Within 40 seconds, close and open the driver's door twice, then insert and remove the key from the ignition again.
4. Within 40 more seconds, close and open the driver's door twice, then insert the key in the ignition and close the driver's door.
5. Turn ignition switch from LOCK to ON to OFF, leaving the key on for one second and off for one second.
6. Remove the key from the ignition lock.

The doors will lock and unlock themselves once.

7. Within 40 seconds, press the lock and unlock buttons on the transmitter at the same time and release.
8. Within 3 seconds, press either switch and release.

The doors will lock and unlock themselves once if the registration was successful. They will lock and unlock twice if the registration failed.

9. If you have other remotes to program, go back to step 7 within 40 seconds.
10. Insert the key in the ignition or open a door to complete registration.

Rewrite mode: To erase all remotes and add new ones:

Start with the key out of the car, driver's door open and unlocked.

1.Insert key in ignition and pull out
2. Within 5 seconds, insert the key in the ignition and pull out again.
3. Within 40 seconds, close and open the driver's door twice, then insert and remove the key from the ignition again.
4. Within 40 more seconds, close and open the driver's door twice, then insert the key in the ignition and close the driver's door.
5. Turn ignition switch from LOCK to ON to OFF twice, leaving the key on for one second and off for one second each time.
6. Remove the key from the ignition lock.

The doors will lock and unlock themselves twice, indicating that you are in rewrite mode.

7. Within 40 seconds, press the lock and unlock buttons on the transmitter at the same time and release.
8. Within 3 seconds, press either switch and release.

The doors will lock and unlock themselves once if the registration was successful. They will lock and unlock twice if the registration failed.

9. If you have other remotes to program, go back to step 7 within 40 seconds.
10. Insert the key in the ignition or open a door to complete registration.

Prohibition mode: To erase all codes and disable wireless door lock function:

Start with the key out of the car, driver's door open and unlocked.

1.Insert key in ignition and pull out
2. Within 5 seconds, insert the key in the ignition and pull out again.
3. Within 40 seconds, close and open the driver's door twice, then insert and remove the key from the ignition again.
4. Within 40 more seconds, close and open the driver's door twice, then insert the key in the ignition and close the driver's door.
5. Turn ignition switch from LOCK to ON to OFF five times, leaving the key on for one second and off for one second each time.
6. Remove the key from the ignition lock.

The doors will lock and unlock themselves 5 times at about 1 second intervals