The objective of this project is simple. We need to add a wireless door contact sensor to our kitchen back door, which is integrated into our Home Control System (HCS). The installation of the door and its location makes it impossible to run wiring of any sort back to any useful location. There is a solid lintel running over the top of the door and a gas pipe in the wall to the right. Access to the wall on the left is very limited by kitchen cabinets and worktop.

In summary we need a solution that meet the following requirements:

• Provides a door contact switch with wireless signalling of changes in state.
• The wireless contact sensor and transmitter is integrated into the door, so that it is not visible from the inside of our kitchen. Failing this is must be very low profile and white in colour, to blend into the door.
• The wireless range needs to be quite long, as the receiver will be approximately 20m away and there will be several solid walls in between the receiver and the door.
• The solution must be extremely reliable as this is the secondary access to our home and reliable alarm operation is required. Ideally the communications will be encrypted and resilient (acknowledged).
• The wireless elements must have a low power usage, to avoid frequent battery changes. 12 months operation is considered a minimum period for the battery life.
• The chosen technology must interface to our existing Home Control System (HCS), i.e. expose an interface that can talk to a PC.