How can I fix my Accenta Intruder Alarm system?

We are a small community facility which has an Accenta + Intruder Alarm system. In the past two weeks it has started to malfunction. When we are inside the large room it continue to emit warning beeps, seemingly picked up when anyone is in range of the sensor. The phone number on our manual is defunct so can anyone recommend a local technician (Brighton East Sussex) who could service the system for us. What is this likely to cost?