Abstract:
Initialization of a sensor for monitoring the structural integrity of a building involves the sensor, a gateway and an installer device. An automated initialization brings the sensor online and enables the sensor for remote monitoring without requiring on-site manual configuration. Through the automated initialization, the sensor joins a logical communication group and a GPS location associated with the sensor becomes remotely accessible by a human network administrator.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application has subject matter related to the following U.S. nonprovisional applications, all having filing dates concurrent herewith, and all of which are incorporated herein by reference: Ser. No. 11/254,377 entitled “DIGITAL COMMUNICATION SYSTEM FOR MONITORING THE STRUCTURAL INTEGRITY OF A BUILDING AND SENSOR THEREFOR;” Ser. No. 11/254,408 entitled “REMOTE CONFIGURATION OF A SENSOR FOR MONITORING THE STRUCTURAL INTEGRITY OF A BUILDING;” Ser. No. 11/254,409 entitled “LINK ESTABLISHMENT IN A SYSTEM FOR MONITORING THE STRUCTURAL INTEGRITY OF A BUILDING” and Ser. No. 11/254,960 entitled “POWER CONSERVING SLEEP MODE FOR A SENSOR FOR MONITORING THE STRUCTURAL INTEGRITY OF A BUILDING.” 
   BACKGROUND OF THE INVENTION 
   In recent years, moisture intrusion has become a more significant concern in facilities management. Moisture intrusion into building walls can result from the failure of weather resistive barriers that are improperly designed or installed, or that have been subjected to prolonged exposure to the elements. If left unchecked, moisture intrusion can lead to an array of serious problems, including mold, rot and structural instability. Business liability arising from moisture related problems has skyrocketed, to the point where many insurers have eliminated or restricted coverage for water damage in their policies. 
   Many moisture intrusion problems that eventually require expensive solutions are detectable through monitoring before they cause acute damage. One known monitoring solution is to install electrical moisture sensors in building walls and periodically test for moisture content. In U.S. Pat. No. 6,377,181, for example, it is described to embed multiple moisture sensors in walls and electrically connect them to a central control unit. The central control unit periodically sends an excitation voltage to each sensor and measures a voltage drop across the sensor, from which the central control unit directly calculates the wall&#39;s moisture content using a resistance curve. 
   This known solution is severely limited in terms of its information yield and overall sophistication. First, the sensors in the known solution are monolithic devices that are only capable of conveying one type of information, namely, a voltage drop indicative of moisture content. These prior art sensors are incapable of conveying information on other parameters indicative of structural integrity, such as temperature and humidity, or operational parameters, such as the sensor&#39;s location, operational state and the time of day. 
   Second, the sensors in this known solution are passive devices that are incapable of initiating information transfer. These sensors must wait to be driven by a periodic excitation voltage to send information to the central control unit. They are incapable, for example, of initiating transmission of an alarm notification to the central control unit upon detecting that a threshold for a parameter relevant to structural integrity has been surpassed. 
   Third, the sensors in this known solution are immutable devices that are not programmatically initializable, configurable or upgradeable. These sensors are not, for example, programmable to bring them online or specify the parameters relating to structural integrity to be monitored, or the operational parameters to be used in monitoring, such as measuring frequency, reporting frequency and alarm thresholds. 
   There is accordingly a need for a solution for monitoring structural integrity of a building that yields more information and provides a more advanced feature set. 
   SUMMARY OF THE INVENTION 
   In one aspect of the invention, a system and method for monitoring the structural integrity of a building is provided wherein the system and method comprise a sensor coupled to the building that communicates structural integrity information to a gateway via a digital communication link. The digital communication link is preferably a bidirectional wireless link that supports packetized data transfer between the sensor and the gateway. By supporting communication between the sensor and the gateway via a bidirectional digital communication link, the sensor is advantageously able to serve as a multidimensional device for reporting numerous types of structural integrity and operational information, an active device for initiating transfer of structural integrity and operational information, and a mutable device that is programmatically initializable, configurable and upgradeable to bring the sensor online and specify the parameters relating to structural integrity to be monitored and the operational parameters to be used in monitoring. Information and parameters relating to structural integrity (hereinafter “structural integrity information” and “structural integrity parameters,” respectively) include, by way of example, information and parameters, respectively, relating to moisture content, humidity or temperature within a building envelope. 
   In another aspect of the invention, such a sensor is made operational by completing a fully automated initialization protocol involving the sensor, such a gateway and an installer device. Upon power up or reset of the sensor, the sensor establishes a first digital communication link with the installer device. Over the first digital communication link, the sensor learns first configuration information from the installer device. The sensor then establishes a second digital communication link with the gateway. Over the second digital communication link, the gateway learns the first configuration information from the sensor. The sensor then establishes a third digital communication link with the installer device. Over the third digital communication link, the installer device learns that the portion of the initialization protocol occurring between the sensor and the gateway was successful and outputs a success indication, such as an audible sound, to indicate successful initialization to a human installation technician. The first configuration information preferably includes a network identifier identifying the sensor with a logical group of devices, and global positioning system (GPS) coordinates identifying the approximate geographic location of the sensor. The gateway preferably passes via the Internet the first configuration information to a Web server accessible by a human network administrator for remotely monitoring the system. Through the expedient of this initialization protocol, the sensor is brought online and enabled for remote monitoring without requiring on-site manual configuration of the sensor. 
   In another aspect of the invention, such a sensor is configurable to report periodic and, optionally, event-driven structural integrity and operational information to such a gateway. Operational parameters stored on the sensor specify what structural integrity parameters to measure, how frequently to measure them, and how frequently to establish a digital communication link with the gateway allowing periodic interrogation of structural integrity information recorded by the sensor. Operational parameters stored on the sensor may also optionally specify alarm thresholds respecting one or more structural integrity parameters that are continuously monitored and which, if surpassed, cause the sensor to establish a digital communication link with the gateway enabling interstitial interrogation of structural integrity information recorded by the sensor. 
   In another aspect of the invention, such a gateway transmits configuration changes to such a sensor over such digital communication links established for interrogation of structural integrity information. Configuration changes are prompted by a human network administrator who may be remote from the gateway and sensors. Using a standard Web browser, the human network administrator preferably visits a system management Web site hosted on such a Web server and specifies the configuration changes to be made, the sensor or sensor group to which the changes are to apply and, in some embodiments, the time the changes are to become effective. The Web server thereafter instructs the gateway to implement changes to the sensors in the specified manner. 
   In another aspect of the invention, in intervals between monitoring and reporting of structural integrity information, such a sensor enters a power conserving sleep mode in which the supply of power is inhibited to nonessential functions, including sensing functions and radio functions. A real time clock on the sensor preferably prompts periodic wake up of the sensor from sleep mode, at which time the supply of power to the sensing functions and radio functions is resumed, if indicated, to perform monitoring and reporting of structural integrity information. 
   In another aspect of the invention, such digital communication links are established between such a sensor and installer device, and between such a sensor and gateway, using a frequency hopping spread spectrum (FHSS) hunt algorithm in which the sensor&#39;s role is limited, thereby minimizing the sensor&#39;s power consumption and extending its battery life. 
   These and other aspects of the invention will be better understood by reference to the following detailed description taken in conjunction with the drawings that are briefly described below. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of a system for monitoring the structural integrity of a building in a preferred embodiment of the invention. 
       FIG. 2  is a block diagram of a sensor in the system of  FIG. 1 . 
       FIG. 3  is a block diagram of gateway in the system of  FIG. 1 . 
       FIG. 4  is a flow, diagram describing, from the perspective of the installer and gateway of  FIG. 1 , a FHSS hunt protocol for establishing a digital communication link in the system of  FIG. 1 . 
       FIG. 5  is a flow diagram describing, from the perspective of a sensor of  FIG. 1 , a FHSS hunt protocol for establishing a digital communication link in the system of  FIG. 1 . 
       FIG. 6  is a flow diagram describing sensor initialization in the system of  FIG. 1 . 
       FIG. 7  is a flow diagram describing sensor reporting in the system of  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   I. System 
   Referring to  FIG. 1 , a system  10  for monitoring the structural integrity of a building is shown. System  10  includes an Internet gateway  20  interconnecting a multiple of sensors  30 ,  40 ,  50  embedded or mounted within a building envelope with a Web server  60  from which system  10  can be monitored by a human network administrator from a monitoring station  70  remote from sensors  30 ,  40 ,  50 . System  10  also includes an installer  80 , which is a handheld mobile device used by a human installation technician to initialize sensors  30 ,  40 ,  50 . In the illustrated example, sensors  30 ,  50  are embedded in the walls of a building  90 , which may be a commercial or residential structure, whereas sensor  40  is embedded in the floor. It will be appreciated, however, that sensors operative within the invention may be embedded in or mounted to any part of a building, including but not limited to walls, floors and roofs. Sensors  30 ,  40 ,  50  measure and record structural integrity information, such as moisture content, humidity and temperature information, proximate the location where they are embedded or mounted. Internet gateway  20  and sensors  30 ,  40 ,  50  communicate over digital communication links  90  established using a wireless local area network (LAN) protocol. Internet gateway  20  and Web server  60  communicate over a wired digital communication link using one or more Internet protocols, such as TCP/IP, Asynchronous Transfer Mode (ATM) or MPLS (Multiprotocol Label Switching). While one gateway  20  and three sensors  30 ,  40 ,  50  are shown in the example shown in  FIG. 1 , a system operative within the invention can include one or more sensors and one or more gateways. 
   II. Sensor 
   Turning to  FIG. 2 , a functional diagram of a representative one of sensors  30 ,  40 ,  50  is shown. Representative sensor  200  includes a processing module  210 , a sensing module  220 , a radio module  230  and a battery  240 . Each module is preferably implemented in a distinct computer chip on a printed circuit board shared by all of the computer chips. Processing module  210  includes a microprocessor  212  and associated memory  214 . Memory  214  stores a firmware image serving as the operating system for sensor  200 , as well as operational parameters configured during manufacturing, initialization and updating of sensor  200  and structural integrity information collected by sensing module  220  during operation. Battery  240  is preferably an M sized lithium battery that powers processing module  210 , sensing module  220  and radio module  230 . Sensor  200  may take any of numerous physical shapes, such as cubical, spherical, cylindrical, conical or pyramidal. 
   A. Sensor Processing Module 
   Processing module  210  communicates with sensing module  220  and radio module  230  via sets of data pins  250 ,  252  and regulates the supply of power from battery  240  to sensing module  220  and radio module  230  via individual power pins  260 ,  262 . With regard to power supply regulation, it is desirable to have a sensor that draws little power so that battery life is minimally impacted by the current that the sensor draws and the dominant factor in battery life is battery aging. This allows sensors to be embedded in areas that have limited or no access for maintenance after the sensor is initially installed, such as wall stud cavities, built-up roofs, and poured concrete slabs. Accordingly, between checks, monitoring and reporting, sensor  200  enters a low power sleep mode. 
   While in sleep mode, processing module  210  inhibits the supply of power to radio module  230  via power pin  262  and inhibits power to sensing module  220  via power pin  260 . Power supply may also be inhibited to functions on processing module  210  except for a real time clock. The real time clock on processing module  210  initiates wake up of modules  220 ,  230  from sleep state to resume periodic monitoring and reporting, as indicated, and to interstitially report any alarm conditions. More particularly, if upon wake up the operative monitoring frequency indicates that it is time to monitor, power is resumed to sensing module  220  via power pin  260  to enable monitoring to be performed. If upon wake up the operative link establishment frequency indicates that it is time to report, or an alarm threshold has been surpassed, power is resumed to radio module  230  via power pin  262  to enable reporting to be performed. In some embodiments, the configured monitoring frequency and link establishment frequency are the same, such that inhibition and resumption of power to sensing module  220  and radio module  230  is synchronized in the absence of alarm conditions. Once the indicated monitoring and reporting are completed, the real time clock is reset and sleep mode is re-entered. 
   In alternative embodiments, monitoring of structural integrity parameters for which alarm thresholds are active is continuous, and consequently the supply of power to sensing module  220  is continuous if any alarm threshold is active. In still other embodiments, a sensing module is divided into multiple sub-modules, each having a distinct power pin, wherein in sleep mode power continues to be supplied to sub-modules that monitor structural integrity parameters associated with an active alarm threshold, but is inhibited to sub-modules that monitor structural integrity parameters that are not associated with an active alarm threshold. Moreover, in such embodiments, surpassing an alarm threshold triggers early wake up from sleep mode for reporting alarm conditions. 
   Numerous operational parameters are stored in memory  214 . Such operational parameters include a sensor identifier (Sensor ID). The Sensor ID is a globally unique 32-bit address that is programmed into a flash memory portion of memory  214  during manufacturing of sensor  200 . The Sensor ID is preferably in the format of “YDDDNNNNN” wherein YY is a decimal two-digit year from zero to 99, DDD is a decimal three-digit day of year ranging from zero to 364, NNNNN is a five-digit decimal serial number. The decimal number created by the above encoding is converted to hex and permanently stored in the flash memory portion. 
   Operational parameters also include an installer identifier (Installer ID). The Installer ID is a 32-bit address that is stored in the flash memory portion of memory  214  by installer  80  during initialization of sensor  200 . Once learned from installer  80 , the Installer ID is used by sensor  200  to identify a received packet as having originated from installer  80 . 
   Operational parameters also include network identifiers (Network IDs). Network IDs are 32-bit addresses that are stored on memory  214 . An installer Network ID is stored on sensor  200  during manufacturing to enable sensor  200  to initiate communication with an installer, such as installer  80 . The installer Network ID is reserved for this purpose. Additionally, an operational Network ID is stored on sensor  200  by installer  80  during initialization of sensor  200 . The operational Network ID is shared by a logical group of structural integrity monitoring and reporting devices operative within system  10  that includes sensor  200 , zero or more other sensors, and one or more gateways. The operational Network ID enables sensor  200  to initiate communication with an in-range gateway that is within the logical device group of sensor  200  (and therefore with which sensor  200  is allowed to communicate), as distinct from an in-range gateway that is in a different logical device group (and therefore with which sensor  200  is not allowed to communicate). Network IDs permit multiple logical communication groups to operate independently within wireless range of one another. Network IDs also allow administrative policies to be applied to a group of sensors by reference to a single identifier. Processing module  210  posses appropriate Network IDs to radio module  230  for local storage and prepending to outbound packets. 
   Operational parameters also include a gateway identifier (Gateway ID). The Gateway ID is a 32-bit address stored in memory  214  by a gateway during initialization of sensor  200 . Once learned from a gateway, the Gateway ID is used by sensor  200  to identify a received packet as having originated from a particular in-range gateway that is within the logical device group of sensor  200 . In this regard, in a given building multiple gateways having the same Network ID as sensor  200  may be active within the range of sensor  200 . Gateway ID allows sensor  200  to distinguish between such gateways during operation in order to maintain session persistence. 
   For the remainder of this detailed description, it is assumed that sensors  30 ,  40 ,  50  (including representative sensor  200 ), and gateway  20  share a Network ID and, as a result, form a logical group of devices within system  10 . 
   Operational parameters also include GPS coordinates. GPS coordinates are stored on memory  214  by installer  80  during initialization of sensor  200 . Gateway  20  then reads the GPS coordinates and transfers them to Web server  60  where the position information is maintained in database records associated with sensor  200 . Thus, when gateway  20  notifies Web server  60  of a problem reported by sensor  200 , the human network administrator can pinpoint the geographic coordinates of sensor  200  and locate the problem. Sensor  200  is preferably powered up or reset near the location it is to be installed in order to ensure a high level of accuracy of the GPS coordinates stored to memory  214 . 
   Operational parameters also include a monitoring frequency, which indicates how frequently sensor  200  measures structural integrity parameters and records structural integrity information to memory  214 . A default monitoring frequency may be stored to memory  214  during manufacturing, and later updated by gateway  20 . 
   Operational parameters also include a link establishment frequency, which indicates how frequently sensor  200 , in the absence of an alarm condition, establishes a digital communication link with gateway  20  for interrogation of structural integrity information recorded by sensor  200 . A default link establishment frequency may be stored on memory  214  during manufacturing, and later updated by gateway  20 . 
   Operational parameters may also include a monitored parameter list. A monitored parameter list may be in the form of a bit mask that specifies which of the several structural integrity parameters sensor  200  is capable of monitoring are presently enabled for monitoring. For example, the monitored parameter list may consist in a three-bit mask wherein the individual bits indicate whether monitoring of moisture content, humidity and temperature, respectively, are presently enabled. A default monitored parameter list may be stored on memory  214  during manufacturing, and later updated by gateway  20 . 
   Operational parameters may also include alarm thresholds. Alarm thresholds specify limits for particular monitored structural integrity parameters that, if exceeded, trigger establishment of a digital communication link with gateway  20  for interstitial interrogation of structural integrity information recorded by sensor  200 . Default alarm thresholds may be stored on memory  214  during manufacturing, and later updated by gateway  20 . 
   During initialization, reporting and updating operations conducted over established digital communication links, gateway  20  and/or installer  80  remotely control access to memory  214  by transmitting packetized direct memory access (DMA) commands to sensor  200 . Segments in memory  214  are mapped to particular functions so that gateway  20  and installer  80  can read or write information by issuing and transmitting to sensor  200  a DMA command that specifies read or write, the memory segment, and the information to be written (in the case of a write command). In response to DMA commands, microprocessor  212  either writes the information to the specified memory segment or reads information from the specified segment and transmits any read information to the issuing one of gateway  20  or installer  80 . To support writing to the flash memory portion of memory  214 , the write command has an “erase before write” option that instructs to erase the flash segment prior to writing the information. 
   The initial firmware image that serves as the operating system for sensor  200  is programmed into a flash memory portion of memory  214  during manufacturing. Replacement firmware images, such as maintenance releases and upgrades, are written in the flash memory portion of memory  214  by gateway  20  using packetized DMA commands. The flash memory portion of memory  214  is partitioned into two sections. When gateway  20  issues a DMA command to write a replacement firmware image, the replacement firmware image is written into the currently unused section of the flash memory, and a program counter on microprocessor  212  is written to force execution of the replacement firmware image. The replacement image then self-checks to make sure it is not corrupted by doing a cyclic redundancy check (CRC) over the full image. If the CRC fails, the replacement image forces a firmware reboot to the previous image. If the CRC passes, the replacement image copies its interrupt vectors to memory  214  so that the replacement image will thereafter execute upon firmware reboot, and forces a firmware reboot to the replacement image. Gateway  20  learns of CRC failures through current firmware version information in packets transmitted by sensor  200  and re-attempts firmware replacement using packetized DMA commands upon learning of such failures. 
   B. Sensing Module 
   Sensing module  220  performs sensing functions for sensor  200 . Sensing module  220  includes probes for measuring structural integrity parameters as instructed by processing module  210  and supplying structural integrity information resulting from such measurements to processing module  210 . Probes include a moisture content probe  222 , a humidity probe  224  and a temperature probe  226 . Moisture content probe  222  preferably includes a circuit for making and performing analog-to-digital conversion of dual voltage measurements indicative of the moisture content of the wall, roof or floor proximate sensor  200 . Processor module  210  stores the digitized moisture content information that is output by moisture content probe  222  in memory  214 . Sensor  200  transmits the moisture content information to gateway  20  during interrogation by gateway  20 , and gateway  20  relays the information to Web server  60 . In some embodiments, moisture content information includes dual voltage measurements made by probe  222  and Web server  60  calculates the moisture content of the wall, roof or floor proximate to sensor  200  by reference to the dual voltage measurements. In those embodiments, Web server  60  calculates an RC time constant from the measurements and calculates the moisture content from a known relationship with the RC time constant. In other embodiments, a moisture content probe may be implemented as a “Wheatstone bridge” circuit whose voltage varies with the resistance of the wall, roof or floor under test. 
   Humidity probe  224  preferably includes a circuit for making and performing analog-to-digital conversion of relative humidity measurements. In some embodiments, probe  224  utilizes a capacitive polymer sensing element in making such measurements. Temperature probe  226  preferably includes a circuit for making and performing analog-to-digital conversion of temperature measurements. In some embodiments, temperature probe  226  utilizes a bandgap temperature sensor in making such measurements. An integrated humidity/temperature sensor, such as the SHT11 digital humidity and temperature sensor marketed by Sensirion AG, may be employed as probes  224 ,  226 . Relative humidity and temperature information returned to processing module  210  from probes  224 ,  226  is stored in memory  214  until interrogation by gateway  20 . 
   C. Sensor Radio Module 
   Radio module  230  provides wireless transceiver functions for a connection oriented wireless LAN communication protocol that enables sensor  200  to communicate with installer  80  and gateway  20 . Features of the wireless LAN communication protocol include wireless link establishment and tear-down and packet formatting. It will be appreciated that these protocol features may be performed by processing module  210 , with radio module  230  supporting processing module  210  with necessary transceiver functions. 
   In wireless link establishment, sensor  200  establishes wireless links with installer  80  and gateway  20  by assuming the link slave role in a low power FHSS hunt protocol. Sensor  200  assumes the link slave role on power up and reset to establish a digital communication link first with installer  80  and then gateway  20  for initialization. Sensor  200  also assumes the link slave role when reporting is indicated by the link establishment frequency or an alarm condition to establish a digital communication link with gateway  20  for interrogation of structural integrity information. The FHSS hunt protocol is preferably implemented on processing module  210  under firmwore control. 
   In packet formatting, sensor  200  packetizes information for transmission into fixed length packets, and prepends to each fixed length packet a header having a source address field, a destination address field and a Network ID field. Each packet is preferably 32 bytes in length. The Sensor ID of sensor  200  is inserted in the source address field. The installer Network ID is inserted into the Network ID field when communicating with installer  80  and the Installer ID of installer  80 , once known, is inserted into the destination address field when communicating with installer  80 . The operational Network ID of gateway  20  is inserted into the Network ID field and the Gateway ID of gateway  20 , once known, is inserted into the destination address field when communicating with gateway  20 . Packet formatting is preferably implemented on processing module  210  under firmware control, except that radio module  230  maintains and prepends appropriate Network IDs on packets. 
   III. Gateway 
     FIG. 3  shows gateway  20  in more detail. Gateway  20  includes a processing module  310 , a radio module  320  for communicating with sensors  30 ,  40 ,  50  and a wireline module  330  for communicating with Web server  60 . Gateway  20  is powered either through an external AC power cord or inline power supplied via wireline module  330 . Processing module  310  includes a microprocessor  312  and memory  314 . Memory  314  stores a firmware image serving as the operating system for gateway  20 , operational parameters configured during manufacturing, initialization and configuration of gateway  20 , configuration information received from Web server  60  awaiting local application or downloading to sensors  30 ,  40 ,  50  and structural integrity information collected from sensors  30 ,  40 ,  50  awaiting uploading to Web server  60 . Processing module  310  communicates with radio module  320  and wireline module  330  via sets of data pins  340 ,  342 . 
   Operational parameters stored on memory  314  include the Gateway ID assigned to gateway  20 , the operational Network ID of the logical group of devices to which gateway  20  belongs, and an address of Web server  60  which may be, for example, an IP address. In other embodiments, the address of Web server  60  may be stored on wireline module  330 . Gateway  20  preferably does not maintain a list of sensors active within its logical communication group. It can be safely assumed that if a sensor is using a Network ID that matches the gateway&#39;s Network ID then that sensor is a member of the gateway&#39;s logical communication group. 
   Radio module  320  provides wireless transceiver functions for a connection oriented wireless LAN communication protocol that enables gateway  20  to communicate with sensors  30 ,  40 ,  50 . Features of the wireless LAN communication protocol include wireless link establishment and tear down and packet formatting. It will be appreciated that these protocol features may be performed by processing module  310 , with radio module  320  supporting processing module  310  with necessary transceiver functions. 
   Gateway  20  establishes wireless links with sensors  30 ,  40 ,  50  by assuming the link master role in the FHSS hunt protocol. Gateway  20  assumes the link master role on power up to announce its readiness to establish digital communication links with sensors  30 ,  40 ,  50 . The FHSS hunt protocol is preferably implemented on processing module  310  under firmware control. 
   Wireline module  330  provides an Ethernet interface for maintaining an “always on” broadband Internet connection to Web server  60 , as well as a PSTN interface with a dial up modem for establishing intermittent dial up connections to Web server  60 . In some embodiments, wireline module  330  includes an embedded Web server supporting Layer  2  and Layer  3  functions, such as TCP/IP and DHCP, and storing the IP address of Web server  60 . 
   IV. Installer 
   Installer  80  is a handheld mobile device having a processing module, a radio module for communicating with sensors  30 ,  40 ,  50 , a wireline module for receiving configuration information from a PC over a serial interface such as an RS-232 interface, and a speaker for making an audible sound to notify a human installation technician of successful initialization of sensors  30 ,  40 ,  50 . Installer  80  is preferably powered by AA sized batteries. The processing module on installer  80  has a processor and a memory storing a firmware image serving as the operating system for installer  80  and operational parameters configured during manufacturing and configuration of installer  80  and awaiting local application or downloading to sensors  30 ,  40 ,  50 . Operational parameters stored on installer  80  include the Installer ID assigned to installer  80 , the installer Network ID, and the operational Network ID of the logical group of devices to which the sensors that installer  80  is responsible for initializing belong. 
   The radio module on installer  80  provides wireless transceiver functions for a connection oriented wireless LAN communication protocol that enables installer  80  to communicate with sensors  30 ,  40 ,  50 . Features of the wireless LAN communication protocol include wireless link establishment and tear down and packet formatting. These protocol features may be performed by the processing module with the radio module supporting the processing module with necessary transceiver functions. 
   Installer  80  establishes wireless links with sensors  30 ,  40 ,  50  by assuming the link master role in the FHSS hunt protocol. Installer  80  assumes the link master role on power up to announce its readiness to establish digital communication links with sensors  30 ,  40 ,  50 . The FHSS hunt protocol is preferably implemented on the processing module under firmware control. 
   After configuration of installer  80  by a PC over the serial interface of the wireline module, a GPS receiver (not shown) can be attached to the serial interface on installer  80  to receive GPS coordinates from an external GPS. This enables installer  80  to provide an approximate GPS location to sensors  30 ,  40 ,  50  during initialization of sensors  30 ,  40 ,  50 . 
   The speaker is operatively coupled to the processing module of installer  80  and is selectively driven by the processing module to sound a series of rapid beeps at the same pitch to indicate successful initialization of a sensor. 
   V. FHSS Hunt Protocol 
     FIG. 4  is a flow diagram describing the FHSS hunt protocol from the perspective of the link master, for example, gateway  20  or installer  80 . In a preferred embodiment, the FHSS hunt protocol uses 127 unique channels in the 902 to 928 MHz frequency band to allow many devices to communicate at the same time without significant signal interference. The channels are chosen pseudo-randomly. Since under the FHSS protocol the link master listens and transmits continuously, whereas the link slave only listens and transmits selectively, gateway  20  and installer  80  are configured as FHSS link masters, whereas sensors  30 ,  40 ,  50  are configured FHSS link slaves, to conserve the battery life of sensors  30 ,  40 ,  50 . 
   The link master, for example, gateway  20  or installer  80 , listens to a channel to verify that it is currently not in use ( 410 ). The link master then transmits a HELLO beacon for approximately 50 ms ( 420 ), then sends a HELLO_END packet to signal the end of the beacon transmission ( 425 ), and then listens for approximately four ms for an ACK packet type from any sensor that heard the beacon ( 430 ). The HELLO_END packet contains information sufficient to identify the link master and the channel number the link master is transmitting on. The channel number is transmitted because it is possible for a sensor to receive a packet on a channel different from that on which it was sent. If no ACK response is received ( 440 ), the link master hops to the next channel ( 450 ) and repeats the process. 
   If the link master receives the ACK to its current HELLO_END ( 460 ), it knows that the link slave, for example, sensor  200 , can hear it and that it can hear the link slave. Based on that knowledge, the link master declares the link state to be “up” ( 470 ). The link slave, however, does not yet know if the link master heard its ACK, so the link master sends a second HELLO_END specifically addressed to the link slave to let the slave know that it heard its ACK packet ( 480 ). When the link slave receives this second HELLO_END, it knows that the link master can hear it and it declares its link state to be “up”. The process of opening a communication session between the link master and link slave is completed when the link slave ACKs the second HELLO_END packet ( 490 ). 
     FIG. 5  is a flow diagram describing the FHSS hunt protocol from the perspective of the link slave, for example, sensor  200 . When the link slave wishes to establish a digital communication link, the link slave hunts for the beacon HELLO packet that the link master is continuously broadcasting ( 510 ). It does this by listening for a carrier for approximately one ms on every channel in sequence using the same pseudo-random sequence as the link master. If a carrier is detected on a channel ( 520 ), the slave continues to listen to the channel to try and receive a HELLO_END packet ( 530 ). After the slave has received a HELLO_END packet, the slave checks to ensure that the packet is from a link master with which link slave wishes to establish a digital communication link. If it is ( 540 ), the link slave transmits an ACK packet type back to the link master containing information sufficient to identify the link slave ( 570 ). Since the slave knows the link master&#39;s identity from the HELLO_END packet, the ACK is specifically addressed to the link master that originated the HELLO_END packet. The slave subsequently receives a second HELLO_END ( 580 ) and sends a second ACK ( 590 ) to complete the process. If the HELLO_END packet is not from a link master with which the link slave wishes to establish a digital communication link ( 550 ), the link slave hops to the next channel ( 560 ) and repeats the process. 
   The link master and link slave use the same seven bit linear feedback shift register to generate a pseudorandom hop sequence. 
   VI. Initialization 
     FIG. 6  is a flow diagram describing a sensor initialization protocol in the system of  FIG. 1 . Sensor  200 , which is a representative one of sensors  30 ,  40 ,  50 , is made operational by completing an initialization protocol involving sensor  200 , gateway  20  and installer  80 . Upon power up or reset, the firmware image on sensor  200  invokes radio module  230  to establish a digital communication link with installer  80  using the installer Network ID and the FHSS hunt protocol ( 610 ). Installer  80  is preferably GPS-enabled at this point. Once the link is established, installer  80  waits for the next valid position to be output from the GPS, and then writes the GPS coordinates and the operational Network ID of the logical communication group in which sensor  200  will participate to sensor  200  using a DMA write command ( 620 ). Installer  80  then closes its session with sensor  200 , but remembers the Sensor ID transmitted by sensor  200 . 
   Sensor  200  then opens a communication session with gateway  20  using the learned operational Network ID and the previously described FHSS hunt protocol ( 630 ). Gateway  20  reads the GPS coordinates of sensor  200  using a DMA read command ( 640 ) and writes the time of day to sensor  200  using a DMA write command ( 650 ). Gateway  20  sends the GPS coordinates to Web server  60  in association with the Sensor ID transmitted by sensor  200  ( 660 ). Gateway  20  ends the communication session with sensor  200 . 
   At that point, sensor  200  sets a “registered” flag in memory  214  indicating it was able to talk to gateway  20 . Sensor  200  then establishes another digital communication link with installer  80  using the Installer ID learned in the previous communication with installer  80  and the previously described FHSS hunt protocol ( 670 ). Installer  80  verifies that the “registered” flag is set and that the Sensor ID transmitted by sensor  200  matches the remembered Sensor ID from the previous session ( 680 ). Installer  80  then sounds a series of rapid beeps at the same pitch indicating successful initialization of sensor  200  ( 690 ). In alternative embodiments, sensors may be equipped with their own beepers or LEDs; however, it bears noting that such beepers or LEDs consume extra power on such sensors. 
   VII. Reporting 
     FIG. 7  is a flow diagram describing sensor reporting within the system of  FIG. 1 . In operation, sensor  200  reports periodic and, optionally, event driven structural integrity and operational information to gateway  20 . After initialization, sensor  200  enters sleep mode and the real time clock on processing module  210  is reset ( 710 ). Sensor  200  wakes up when the timer expires ( 715 ) and monitors structural integrity information if the time for monitoring is indicated by the monitoring frequency on memory  214 . Sensor  200  then determines if an alarm threshold has been surpassed. If so ( 720 ), sensor  200  establishes a link with gateway  20  using the FHSS hunt protocol for reporting structural integrity information via interstitial interrogation ( 725 ). Interrogation is achieved through the issuance by gateway  20  of packetized DMA read commands and the fulfillment by sensor  200  of those commands. After such interrogation, sensor  200  returns to sleep mode and the real time clock is reset. If no alarm threshold has been exceeded ( 730 ) but the link establishment frequency indicates time to report ( 735 ), sensor  200  establishes a link with gateway  20  using the FHSS hunt protocol for reporting structural integrity information via periodic interrogation ( 740 ) prior to returning to sleep mode and resetting the real time clock ( 745 ). If the link establishment frequency does not indicate time to report ( 750 ), sensor  200  returns to sleep mode and the real time clock is reset without interrogation. Of course, in some embodiments there are no alarm thresholds. In embodiments without alarm thresholds, the step indicating to check whether an alarm is exceeded is bypassed. 
   Gateway  20  relays learned structural integrity information to Web server  60  in periodic or event driven reports using a known address of Web server  60 , such as an IP address. In some embodiments, structural integrity information is transmitted to Web server  60  over an “always on” broadband Internet connection. In other embodiments, gateway  20  relies on a dial up Internet connection. In dial up embodiments, gateway  20  stores the structural integrity information in a local cache for a time before periodically dialing up the Internet service and uploading the information to Web server  60 . However, gateway  20  also maintains local alarm thresholds that trigger immediate dial up of Web server  60  if exceeded. Moreover, in dial up embodiments, gateway  20  preferably receives power from the phone line to render system  10  invulnerable to AC power outages within building  90 . 
   VIII. Configuration Changes 
   Gateway  20  also utilizes digital communication links established for interrogation to transmit configuration changes to sensor  200 . Whenever sensor  200  establishes a digital communication link with gateway  20  for interrogation of structural integrity information, gateway  20  may, in addition to interrogating sensor  200  for structural integrity information using DMA read commands, issue DMA write commands to sensor  200  that cause sensor  200  to store configuration changes in specified segments of memory  214 . In some embodiments, configuration changes are written during the first interrogation after receipt of the configuration information from Web server  60 . In other embodiments, configuration changes are written during an interrogation that is at or near a time specified by the human network administrator, and during the first interrogation after receipt of the configuration information if no time is specified. In either case, gateway  20  advantageously puts into dual use preexisting digital communication links between gateway  20  and sensors  30 ,  40 ,  50  that are established independently of configuration changes. 
   The human network administrator preferably initiates configuration changes to gateway  20  and sensor  200  from a standard Web browser on monitoring station  70 . The human network administrator preferably visits a system management Web site hosted on Web server  60  and inputs information sufficient to identify the configuration changes to be made, the target device and, in some embodiments, the time the changes are to become effective. Web server  60  generates a command that describes the change (i.e. sensor or gateway, firmware or other configuration change) and target device (i.e. gateway  20 , sensor  200  or sensor group  30 ,  40 ,  50 ). In response to a next contact by gateway  20  pursuant to an upload of structural integrity information or a “server ping” initiated by gateway  20  after a period of inactivity, Web server  60  instructs gateway  20  to implement the specified changes at the specified time, if any. 
   It will be appreciated by those of ordinary skill in the art that the invention can be embodied in other specific forms without departing from the spirit or essential character hereof. As one of numerous examples, rather than continuous remote monitoring of gateway  20  over the Internet, “on demand” local monitoring may be conducted by plugging a PC into the Ethernet interface on gateway  20  and retrieving structural integrity information cached by gateway  20 . The present description is therefore considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the appended claims, and all changes that come within the meaning and range of equivalents thereof are intended to be embraced therein.