If your burglar alarm system is monitored with police response you will get 2 different types of activation.

The first is an 'unconfirmed' alarm, which means one detector has activated. This could be a false alarm or a genuine intruder. The monitoring centre will call you or the key holder to tell you this. You will have to go and check the property for any signs of an intruder.

The second is a 'confirmed' alarm, which means two detectors have activated. This is unlikely to be a false alarm. It could be someone forgetting the code and walking through the house or a genuine intruder. The police are alerted for a 'confirmed' alarm along with you or the key holder.