98 Rodeo factory alarm question ?

When my wife gets to her place of destation, she places the vehicle in park, turns the key to the off postion, she then gets out and goes the to the back door opens it, takes or son out of the vehicle, then she close the back passenger door, then open the front pass. door and locks the doors, when she comes back to the vehicle, and unlocks the door the alarm sounds honk honk honk.

When I get to out of  the vehicle i will  place it in park, shut it off, open the drivers door lock the doors, reach back and unlock my sons door, then i take my son out , and lock his door,   then when i unlock the passenger door it honks one time, and sometimes it does not sound at all

I'm wondering what would cause this?

 My wife said that when she locks the doors the way I do, she says it will still set it off, honk honk honk

Thanks

We just recently purchased the rodeo, and in the manual it writes about there being a remote for it which I did not receive when I purchased the vehicle,

Just wondering if I would be able to add a remote and how I would go about getting one