Seat Alhambra car alarm problem

I had a similar problem with my Volvo. It sounds like the anti-theft system's configuration. A power failure could have corrupted the alarm system's memory. The alarm sensor might be faulty, or the connections to the alarm system could be bad. Also, check the battery. A weak battery can cause errors in electronic control units.

Optical locking What is it and how does it affect the car alarm

By 'optical locking', I think the technician means the visual confirmation from the car's lights when locking or unlocking. The system might be set up so a fault in the indicator circuit triggers the alarm. I tried to give some basic advice, but you should get help from professionals. Modern car electrical systems are complex, so a workshop with the right tools would be best. The cost you mentioned sounds like a basic diagnostic and recoding.

The workshop discovered the car alarm was coded to activate the optical locking. They recoded it, and it's now working. The cost was 45€, thanks for the help.