A while back, I helped a friend set up a system for something similar. Basically, we connected a motion detector to a mobile phone, and to keep it simple, we used a service that lets you send and receive SMS online free Australia. This way, the detector could send an SMS to the caretaker’s phone whenever it was triggered, without needing a full phone plan. It was easy to set up and gave us some peace of mind. It might be a good option for your brother too.