How to disable a anti theft alarm in a 1999 Nissan Pathfinder

I'm having the same issue with my 1999 Nissan Altima. The thing is I don't have a key fob! I have 2 factory issued keys that came with the car. I bought the car a little over a month ago, and it ran beautifully, until the battery died. It turned out that my alternator went out. After replacing the alternator and insuring that no wires were crossed or touching..... I charged and connected the negative cable back to the battery, and my hazards and dash lights began to blink! The car registered that the key was in the ignition, and that beeped, but that was it. After 15 seconds the flashing would stop, only to resume if I tried to start my car again. If you have already found a solution to this issue, I would love to hear it.

While car is running and car is beeping get out driver's side door, lock and unlock the door with key 3 to 5 times in the alarm should stop