建立無線運動檢測系統

　　無線技術是實現易于使用的運動檢測系統的關鍵。有一系列廣泛的無線技術用于將運動探測器連接到中心集線器，從ISM頻段到ZigBee，到Wi-Fi和其他因特網連接的協議，但無線鏈路的可靠性非常重要。從制造商如Atmel、Silicon Labs和恩智浦半導體器件，可以用不同的方式來提供無線連接到中央集線器作為一個強大的運動檢測和報警系統的一部分。

　　運動探測器變得越來越普遍，但結果是對各種惡意攻擊變得更加開放。這對運動傳感器系統的設計產生了影響，無線元素的關鍵是確保一個安全而靈活的實現，它適合于實際應用——實際上在有入侵時能夠標志。

　　在這種系統中，無線技術以多種不同的方式被使用。許多運動傳感器包括無線鏈路回到中央集線器，但這為開發人員提供了更多的技術和安全選擇。無線電波本身甚至被用作運動傳感器，比被動紅外傳感器提供更多的能力。

　　The problem is highlighted by recent examples where thieves have drilled through walls to avoid motion sensors. One way around this problem has been developed by a US startup called Xandem. It is using the fact that the presence of a body reduces the penetration of radio waves， and so can be used to detect motion. Its tomographic motion detection （TMD） technology can sense through walls and obstructions， and senses over areas that are otherwise extremely difficult to cover. It can remain completely hidden from view， enhancing both the security and the aesthetics of the installation.

　　A Xandem TMD system is built with two kinds of devices： nodes and a processing unit. Multiple nodes surround the area where motion is to be detected， using mesh networking technology that senses when objects move within the area of the mesh， even through walls and obstructions. Each node is not a sensor; the mesh network connecting the nodes is the sensor. The processing unit is a gateway with normally-closed relays that connect to any standard panel to act as the hub.