When I unlock my 2008 Superb the alarm stays active and when open doors it goes off, and I can't unlock car remote, always must unlock manually, what could be cause of that? 

i don't have an alarm,

but please check topic:

 

'Water Ingress Problem'........SOLVED!

 

it can be due to wiring.

 

 

Firstly, you can check the battery in your key

BR

Are you locking it remotely?

Remote lock enables alarm and deadlocks at first lock button click.  If you click lock twice it disables alarm and deadlocks.  You can see if alarm is armed by looking at the LED on the door lock on driver's side.

If your unlock remote button doesn't work then you will trip the alarm when you unlock car with key, as alarm is only deactivated by remote control.

 

I think if you are quick and get keys into ignition and turned on within 5 seconds the alarm won't go off.