Ok, dumb ass question here.

Bought the car with 65,000. Uses the factory key fob.

If I'm out of the car, the doors auto lock after about 20-30 seconds, If i'm in the car, they don't. As far as I know, and the previous and first owner states, there is no aftermarket alarm. I can find no alarm units anywhere. The only thing I can think of is it's the LoJack installed when first sold by the dealer on the car. Does the Lojack do that? Is it controllable/programable?

 

Mine does the same thing, and I'm pretty sure I don't have an aftermarket alarm. I think all s2000s auto lock from the factory. My car is a '00 if it makes any difference.

 

Does it do it if you are in the car, without the key in the ignition? Mine doesn't. Is it sensing me sitting in the seat?

 

its like any other car, if you unlock the car and you dont open the doors it will auto lock

 

Do you mean if you don't keep the doors open? I mean, if I unlock, open, and then close the doors, it will auto lock.

 

That is correct. However, that is not the situation the OP is describing.

Posted this in the other thread: no.

 

Sounds like you have an OEM alarm that in a passive arming mode. You should be able to change that to manual mode on the OEM control module, which is mounted under the driver seat.
[attachment=22754:OEM alarm.bmp]