I found this online! Has anyone tried?
How to Program A Nissan Keyless Entry Key FOB remote
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If you have lost your keyless entry remote or just want to add keyless entry to your Nissan, you can do it yourself. The dealer will charge you several hundred dollars to do this but all you need is the key fob remotes and about 10 minutes of free time. Follow these steps to program your keyless entry on a Nissan.
The first step is to actually get the remotes. If you already have the remotes, proceed to step 2. If you do not, get on eBay and find the remotes for your year and model Nissan. You can usually get them for about $50 a pair, shipped. This is at least half of what the dealer will charge you.
Open the drivers side door of the vehicle and get in the vehicle. Close the door. Press the lock button on the drivers side door to lock all the doors.
Insert your key into the ignition and remove it at least 6 times. It may take up to 10 times. This needs to be done in a good pace, but not too fast. At least 6 times within 10 seconds is about right. If you have done it right, you will see the hazard lights flash twice.
Once you see the hazard lights flash twice, the car is now in program mode. Insert the key back into the ignition and turn it to ACC. Push any button on your keyless entry FOB remote ONCE. This should be done within 5 seconds of turning the key to ACC. You should notice your hazards flash again. If you have another remote to program proceed to step 5, otherwise turn the key off and remove it. The remote should now be programmed.
If you have another keyless entry remote to program unlock the door with the drivers side power lock and then lock them again. Press any button on the next remote. Turn the key back to the original position and remove the key. The remotes should now be programmed.