where is the alarm unit located in the superb mk1?

I don't have water ingress or any cables damage. hence will try to replace the unit that control remote doors unlocking. 

under the driver seat is only one unit but it looks that it only controls the seat.

The alarm sounder is in the plenum chamber, on the driver's side of the battery, near the brake vacuum booster.  Remove the plastic cover that runs across the car to expose the battery.  The sounder is mounted low down where it's not very easy to access.