The Intruder Boxes have a PIR detector which can detect movement of objects which have a temperature which is warmer than the ambient surroundings. A human being for example!
They also incorporate a humidity detector and a temperature sensor. This can be very useful for monitoring any humidity in the boat during the winter and ensures any heaters and de-humidifiers are working properly.
Up to 6 boxes can be added to the system as with other peripheral boxes. Connection can be by network cable or RF. If RF is being used then the box needs either a DC supply of 10-36v, or a DC 5v supply on a micro USB connector. When in a lounge area this could easily be a phone charger type of supply.