Build and design light detection circuit to operate remote relay.

I want to covertly monitor the opening of a outside box on the perimeter of my property with the purpose of operating a contact at my main house. I see this working in 3 stages as follows: 1)A covert weatherproof battery-powered peep-hole light detection circuit mounted on the underside of the monitored box, transmitting to 2) another internal box 10m away. The second box has 220Vac and then this signal is transmitted to a 3) reciever the the main building 200m away where it opens a 220Vac contact. These last two elements do not need to be weatherproof or covert. Entire sensor circuit is to be matchbox sized, covert and weather proof. A magnetic mount is preferable. The light sensor is to unobtrusive, and small to as to be unnoticeable as it fits in the small hole drilled in the steel box. the box is constructed of 3mm thick steel. The unit should be battery powered with at least a year's life span, before the battery has to be changed. ( But the longer the better). So the design should be such that there is no idle power. The box will be open for an hour a year in total. The second and third elements can be off the shelf transceivers, it is the first stage that I am really interested in.