Vauxhall Vectra Siren Communication Fault

Could be a few things, but a bad connection is a good place to start. Have you checked the fuses related to the alarm? Is the error code specific, or just a general communication fault?

Fuses are fine. The code reader just states 'Siren communication fault'. Could a complete siren replacement be necessary, or is it premature to assume that?

A siren replacement is possible but I'd inspect the wiring and connections thoroughly first. Given the generic code, it's hard to say definitively. Have you considered taking it to a workshop to rule out more complicated causes?

Thanks, I appreciate the feedback. I booked a diagnostic at the workshop as suggested. Turns out, after checking all the connections, there was a defective plug to the alarm siren that needed replacing. Job done for 95€