Abstract:
A freeze detection device that sends a wireless freeze-alert signal when a water freeze condition is detected. The device allows ready installation in areas where traditional freeze detection equipment would require significant effort and expense. The device provides freeze-detecting functionality with very small power consumption, allowing long lasting sensing capability and low maintenance.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of U.S. Provisional Application 60/474,678 filed May 31, 2003. 

   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not Applicable. 
   REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISK APPENDIX 
   Not Applicable. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to freeze sensors that function to detect potential fluid freezes in water pipes and wirelessly transmit a freeze alert signal. 
   The freezing of pipes in houses and other structures has historically proven to be a significant problem in cold climates. In most cases, pipes in attics, crawl spaces, and other poorly heated or un-heated areas or extremities of the structure will be subject to freezing when the water is left still during prolonged periods of cold. 
   The ability to detect freeze conditions before freeze onset is an important part of any system that seeks to actively prevent freeze damage. However, the optimal locations for sensing near-freezing temperatures or other freeze conditions are often in areas that would be impractical to reach with AC electrical power. Therefore, the freeze sensor should be self-powered, using a battery or other similar means. The optimal sensing location, such as in a crawl space or basement, may also be remote from areas where a user could easily monitor or avert freeze conditions. In many instances, freeze prevention consists of opening a faucet or a fixture to let water flow through the pipe or pipes in question. Therefore, the ability of the freeze sensor to wirelessly transmit a freeze threat signal to a remote location provides for more flexible placement of sensors and a more user-accessible freeze alert system. 
   In the past, three general methods of freeze alarms have tried to provide pipe-freeze warnings: 
   1. A self-contained freeze alarm consists of a battery, temperature sensor, and an audio alarm within one housing. Such a device is shown in U.S. Pat. No. 4,800,371 issued to Arsi in 1989. Since the sensing location is typically far from the heated living space of the building, the alarm may be difficult for a user to hear. If the alarm were made powerful enough to be easily heard, then the batteries powering the alarm would be quickly drained. Further, such an alarm cannot provide freeze condition signals to an automated freeze-prevention system. 
   2. A household thermostat, with integrated temperature sensor, sends a “low heat” message to a monitoring service if the sensed temperature drops below some threshold temperature. Because the thermostat is not located in the unheated areas of the building where water pipes are most likely to freeze, the sensed temperature at the thermostat gives an extremely inexact indication of freeze likelihood, resulting in either frequent false alarms or alarms issued too late to prevent water freezing. 
   3. A water-activated alarm that provides an alarm in the event of a water leak is shown in U.S. Pat. No. 5,655,561 issued to Wendel et al on Aug. 12, 1997. Such a device provides an alert too late, after freeze damage has already occurred. 
   SUMMARY OF THE INVENTION 
   It is an object of this invention to provide wireless freeze-threat information necessary to prevent the freezing of water within water-carrying pipes of a building. It is a further object of this invention to permit more flexible placement of freeze sensors within a building and therefore provide easier sensor installation and increased reliability of freeze threat detection. It is another object of the present invention that the wireless signal provided by the present invention can be used for a central alert system, building monitoring system, or an automated freeze-prevention system capable of receiving wireless signals. 
   The present invention allows for an easy and cost effective installation of a freeze condition sensor by using wireless transmission of freeze sensor data, together with internal analysis of sensor data to intelligently control data transmission timing. Transmitted freeze sensor data may activate a freeze prevention system or device such as a flow activation device or heating device. Alternatively, transmitted freeze sensor data may be received by a remote alarm and thereby alert a building occupant about the freeze condition. Transmitted freeze sensor data may also provide notification to a home monitoring service about the freeze condition. 
   In particular, the present invention contains, as described in the embodiments, an electronic circuit that periodically samples the sensed ambient air temperature in the vicinity of a pipe of concern. The sample interval is predefined in the sensor or is configured by the user through an interface on the sensor housing or through remote command signals. The circuit, which contains a microprocessor, compares the measured temperature with two separate set point temperatures, “freeze threat” and “freeze safe”, and decides on whether to transmit a signal indicating “freeze threat” when the sampled temperature has dropped below the predefined “freeze threat” set point or to transmit a signal indicating “freeze safe” when temperature has risen above the predefined “freeze safe” set point. The set point temperatures are predefined in the circuit or are configured by the user through an interface on the sensor housing, or through remote commands. 
   The freeze sensor&#39;s transmission reliability can be improved by transmitting the freeze condition signal multiple times to ensure that the remote system or device receives the signal. In addition, said transmission reliability can be improved by equipping the freeze sensor with a receiver for receiving a confirmation signal from the remote system for which said freeze sensor provides freeze sensing service. In the latter case, the freeze sensor attempts to re-transmit its signal if an expected confirmation is not received. 
   The present invention provides both a method and a device for use in connection with a climate control system, plumbing control system, alarm system, or building monitoring system capable of receiving wireless signals. When used in combination with a climate control system or plumbing system, the freeze sensor functions to prevent water freeze-up within the water carrying pipes of a building. When used in combination with an alarm system or building monitoring system, the freeze sensor functions to provide an alert about impending water freeze-up conditions. 
   Several advantages of the present invention are:
     (a) Provide easier and faster installations of freeze condition sensors for alert or freeze prevention systems. These freeze sensors are easily installed at any location within about 100–200 feet from the receiver unit;   (b) Allow ready installation in areas where traditional freeze detection equipment would require significant effort and expense;   (c) Provide for ease in retrofit installations, integrating with already installed alarm systems, plumbing systems or environmental control systems capable of receiving wireless signals;   (d) Provide freeze-sensing functionality with very small power consumption, allowing long-lasting sensing capability and low maintenance. This is accomplished by the intelligent transmission of the freeze condition signal only when necessary, which enables at least one year of operation with power supplied by small, inexpensive batteries;   (e) Provide a low battery alert to remind the user of an impending need for battery replacement, enabling uninterrupted service.   

   While the principal objects and advantages of the present invention have been explained above, a more complete understanding of the invention may be obtained by referring to the description of the preferred embodiment and an alternate embodiment that follow. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of a typical arrangement of the preferred embodiment of the present invention, showing key functional components including a typical sensor, in this instance a thermal sensor as the sensor component, a micro-controller unit (MCU), a user interface, and a transmitter module. 
       FIG. 2  is a perspective view of the preferred embodiment of the present invention, illustrating both a freeze sensor housing and the user interface. 
       FIG.3  is a temporal view of the freeze condition signal of the preferred embodiment of the present invention, illustrating the freeze condition signal generated by the freeze sensor as a function of the periodically measured temperatures, sampling time interval, and two setpoints. 
       FIG. 4  is a flow chart of the internal decision logic of the freeze sensor according to the preferred embodiment of the present invention. 
       FIG. 5  is a block diagram of a typical arrangement of one embodiment of the present invention, showing the use of a transceiver capable of two-way communication. 
       FIG. 6  is a perspective view of one embodiment of the present invention, illustrating a freeze sensor housing for the components of  FIG. 5  residing therein 
       FIG. 7  is a flow chart of the internal decision logic of one embodiment of the present invention. 
       FIG. 8  is a block diagram showing a plurality of the present invention, in its preferred embodiment, being used as sensing modules for an existing alert system. Said alert system typically includes a transceiver module, a micro-controller unit, and an alert module. 
       FIG. 9  is a flow chart of the freeze alert decision logic, adapted into an existing alert system as in  FIG. 8 . Said decision logic is evaluated by the micro-controller of the alert system when said micro-controller receives a signal from one of the freeze sensors. 
       FIG. 10A  is a cross-sectional view of the preferred embodiment of the invention, showing a typical sensor and transmitter module configuration, in this instance, a thermal sensor as the freeze detection sensor. 
       FIG. 10B  is a cross-sectional view of one embodiment of the invention, showing a pressure sensor as the freeze detection sensor. 
       FIG. 10C  is a cross-sectional view of one embodiment of the invention, showing a non-integrally housed sensor and transmitter. 
       FIG. 10D  is a cross-sectional view of one embodiment of the invention, showing the combination of more than one freeze condition sensor connected to the transmitter module, in this instance, a thermal sensor and pressure sensor. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention provides a wireless freeze condition signal indicating whether a water pipe is under the threat of freezing. Such signal can be used to provide an effective alert or as input to an automated freeze prevention system. For illustration purposes, without limiting the scope of the invention, the drawings use a thermal sensor as the freeze detection component. The present invention is shown being used as one or more sensing modules for a remote alert system. These illustrations should not be construed as limiting the scope of the invention to the illustrated embodiments. 
   Referring now in detail to the drawings, the reference numeral  20  denotes generally a freeze sensor in accordance with the preferred embodiment of this invention capable of one-way communication from the freeze sensor to a remote system; the reference numeral  120  denotes generally a freeze sensor in accordance with one typical embodiment that is capable of two-way communication between the freeze sensor and remote system. The freeze sensor is designed with conventional microelectronics including the use of off-the-shelf microprocessor and radio-frequency transmitter components using existing technologies. It is envisioned that a conventional nine-volt battery would provide sufficiently long-lasting (more than a year) electrical power for the device. 
   Referring now to  FIG. 1 , shown is a block diagram of freeze sensor  20  according to the preferred embodiment of the present invention, comprised of a set of key functional modules. In particular, freeze sensor  20  contains a freeze detection sensor  2 , in this instance, a thermal sensor, which is connected to an A/D converter  4  which is in turn connected to a micro-controller unit (MCU)  10 . Two sets of interface means,  12 , and  14 , are connected to MCU  10  for configuring network ID (NID) and unit ID (UID). A push button  28  is also connected to MCU  10  for toggling between ‘test’ and ‘service’ operation modes. LEDs  18 ,  22 ,  24 , and  26  are operatively connected to MCU  10  to provide visual feedback about functional states of the device. In addition, MCU  10  is operatively connected with RF transmitter  16  that is responsible for transmitting signals to a remote system. Further, MCU  10  (such as an MSP430 product by Texas Instruments Inc.) contains a built-in EEPROM  6 , for storing a data-analysis and decision-logic program, and a RAM  8  for storing runtime values. 
   Continue on  FIG. 1 . Through interface modules  12  and  14 , a user can configure the NID and the freeze sensor UID, respectively. These IDs along with the freeze state (denoted by FREEZE — STATE hereafter) are sent by transmitter  16  as RF signals upon a request by MCU  10  based on an evaluation of a logic program. The remote system of the same NID, upon receiving data from a freeze sensor, uses the NID to ensure that it processes only those data sent from devices in its own network and not those from similar devices of a neighboring network. The remote system uses the UID to identify specific information such as the location of the freeze-threat condition. 
   Referring next to  FIG. 2 , shown is a perspective view of freeze sensor  20  according to the preferred embodiment of the present invention, with on-off switch banks  12  and  14  for configuring the NID and the UID, respectively. LED  18  lights up when the FREEZE — STATE is ‘1’. LED  22  lights up when data transmission is active. LED  24  lights up when battery power is present and sufficient, and blinks slowly when battery power is low. LED  26  lights up when freeze sensor  20  is in ‘test’ mode and is off when freeze sensor  20  is in normal ‘service’ mode. Pushbutton  28  is for toggling between ‘test’ and ‘service’ modes. There is one set of air holes  32  on either side of the front of the housing. They ensure that the thermal sensor senses ambient air temperature. 
   Referring now to  FIG. 3 , shown is a temporal view of temperature samples  41  represented in coordinates of temperature  3  versus time  5 , a temporal view of the corresponding internal FREEZE — STATE signal  43 , and a temporal view of the corresponding transmission state, according to the preferred embodiment of the present invention. Every τ s  33 seconds MCU  10  samples the current value of sensor module  2 , evaluates a decision logic (illustrated in  FIG. 4 ), and sets the internal FREEZE — STATE  43 . The value of FREEZE — STATE is either ‘0’ for freeze-safe state  35  (i.e., no impending freeze condition), or ‘1’ for freeze-threat state  37  (i.e., impending freeze condition exists). Following a state transition (i.e., changing from ‘1’ to ‘0’ or vise versa) of the FREEZE — STATE signal, a preset number of RF transmissions spaced by a transmission time interval, τ x , are performed as shown in the ‘transmission active’ temporal view  45 . 
   It is understood by those skilled in the art that the sampling time interval τ s    33  and the transmission time interval τ x    39  could be made user-configurable by providing additional interface means. However, for simplicity and without losing functional validity and practicality, it is assumed that both time intervals are predefined according to the preferred embodiment of the present invention. Usually, the sampling interval τ s    33  is in the range of 1 to 5 minutes for ‘service’ mode and 10–20 seconds for ‘test’ mode; the transmission interval τ x    39  is about 1 minute for ‘service’ mode and 5–10 seconds for ‘test’ mode. 
   Continue on  FIG. 3 . Shown in  FIG. 3  are two predefined temperature setpoints: T threat    7  and T safe    9  with T threat    7  being lower than T safe    9  usually by about 1–2° C. When MCU  10  detects at sample time t threat    15  that temperature has just dropped below T threat    7 , it raises the alert flag by setting its internal FREEZE — STATE signal to ‘1’  37  and then requests transmitter  16  to send the FREEZE — STATE value along with the NID and UID. Since the preferred embodiment assumes one-way wireless communication from the freeze sensor  20  to the remote system, multiple transmissions are made to increase communication reliability. For simple illustration without loss of generality, the FREEZE — STATE value ‘1’  37  is shown herein being transmitted three times, separated by transmission interval τ x    39 , as indicated by the transmitted freeze state signal  17 . Once the FREEZE — STATE value ‘1’ has been transmitted three times, further temperature samples do not trigger signal transmissions until the temperature crosses above the setpoint T safe    9 . When MCU  10  detects at sample time t safe    25  that temperature has just risen above the setpoint T safe    9 , it sets the FREEZE — STATE to ‘0’, and requests that transmitter  16  send the updated FREEZE — STATE value along with NID and UID. Again, for increased reliability of communication, the FREEZE — STATE value ‘0’ is sent three times as shown by the transmitted freeze state signal  27 . Those skilled in the art know that one setpoint could be used instead of two separate ones. However, one setpoint could introduce oscillation to the FREEZE — STATE signal when ambient temperature stays in a narrow range around the single setpoint. Therefore, the use of two separate setpoints is preferred for increasing freeze sensor reliability and reducing or eliminating false alerts. 
   Referring now to  FIG. 4 , a flow chart depicting the internal logic periodically evaluated by MCU  10  of freeze sensor  20 , according to the preferred embodiment of the present invention. It should be noted that prior to the start of evaluating said logic program, the NED and UID have been stored in internal RAM  8  of MCU  10 . It should also be noted that the temperature sampling interval τ s    39 , the transmission interval τ x    19 , and the number of transmissions N x  for each state change of the FREEZE — STATE signal are predefined by the freeze sensor and are also stored in the internal RAM  8  of MCU  10 . 
   The program control starts at functional blocks  40  and  42  to initialize variables for the logic program execution loop, where variable t x  represents the time when the freeze state signal was last transmitted and variable t s  denotes the time when the temperature was last sampled. The periodic logic evaluation process starts with a sleep of δ seconds at block  44 , where δ denotes the time interval in which the logic program is periodically executed. It should be noted that the program execution time interval δ, usually a few seconds, is much smaller than both the sampling time interval τ s  and the transmission time interval τ x . After waking up from block  44 , control continues at block  46  where the current time t is read from the micro-controller&#39;s internal clock. If the time span elapsed since the temperature was last sampled is longer than the preset sampling time interval τ s , as in the case of the positive outcome of operational block  48 , control advances to functional block  54  where the current temperature, T current , is read and then to block  56  where the last sample time t s  is updated with the current time value t. 
   Next, the logic flow continues to operational block  58  where the current temperature, T current , is compared with the setpoint T threat . If T current  is lower than T threat  but T prev  is higher than T threat , as in the case of the positive outcome of operational block  60 , the temperature has just dropped below T threat , which indicates that the freeze state has just changed from freeze safe to freeze threat. Therefore the following series of actions ensue: set FREEZE — STATE to ‘1’ at block  62 ; prepare for the next round of logic evaluation by setting T current  value equal to T prev  at functional block  64 ; initialize transmission counter N to ‘0’ at functional block  66 ; issue ‘TRANSMIT DATA’ command to the transmitter at functional block  68  where the FREEZE — STATE value is transmitted along with the pre-configured NID and UID; update the last transmission time t x  at functional block  70  to hold the current time value t; and increment the transmission counter at block  72 . Then control proceeds to block  44  to start the next cycle of logic evaluation. 
   If T current  is greater than T safe  but T prev  is lower than T safe  as in the case of the positive outcome of operational block  76 , the temperature has just risen above T safe , which indicates that the freeze state has just changed from freeze threat to freeze safe. Therefore control proceeds to set FREEZE — STATE to ‘0’ at block  78  followed by executing functional blocks from  64  through  72  as described above and then proceeds to block  44  to start the next cycle of logic evaluation. 
   A negative outcome of operational block  60 ,  74 , or  76  indicates that the sensed temperature has not crossed a threshold, so control advances to sleep δ seconds at block  44  as the start of the next cycle of logic evaluation. 
   Continue on  FIG. 4  at operational block  48 . If the time elapsed since the last temperature sample does not exceed the sampling time interval τ s  as in the case of the negative outcome of block  48 , control proceeds to block  50  to check whether the time elapsed since the last transmission exceeds the transmission time interval τ x . The positive outcome of block  50  leads to operational block  52  where the number of transmissions, N, is compared to the maximum number of transmissions, N x , allowed for each state change (i.e., switching from ‘1’ to ‘0’ or vise versa) of the FREEZE — STATE signal. If the transmission counter N is less than N x , control advances to the following actions: issue “TRANSMIT DATA” command at block  68  requesting that the transmitter send the current FREEZE — STATE value along with the NID and UID; set last transmission time t x  to the current time value t at block  70 ; then increment the transmission counter at block  72 . Then control completes the current cycle of the logic evaluation upon the completion of block  72  and proceeds to block  44  to begin the next cycle. If the time elapsed since the last transmission is less than the transmission time interval τ x  as in the case of the negative outcome of block  50  or if the current FREEZE — STATE has been transmitted at least N x  times as in the case of the negative outcome of block  52 , control advances to block  40  to start the next cycle. 
   Referring now to  FIG. 5 , shown is a block diagram of a freeze sensor  120  according to an alternate embodiment of the present invention, comprised of a set of key functional modules. In particular, freeze sensor  120  contains a freeze detection sensor  2 , in this instance, a thermal sensor, which is connected to an A/D converter  4  which is in turn connected to a micro-controller unit (MCU)  10  that contains built-in EEPROM  6  for storing a data-analysis and decision-logic program and RAM  8  for storing runtime values. LEDs  18 ,  22 ,  24 , and  26 , which provide visual feedback on functions of the freeze sensor, are also connected to MCU  10 . RF transceiver  116 , also connected to MCU  10 , enables two-way communication between the freeze sensor  120  and the remote system. Messages sent from freeze sensor  120  are either a freeze state signal or a low-battery warning signal. Each signal is transmitted along with the network ID and unit ID. Messages received from the remote system are one of the following types: a confirmation of a received signal, a command for configuring network ID, unit ID and temperature sampling period, or a command to start operation of ‘test’ mode or ‘service’ mode. 
   Next referring to  FIG. 6 , shown is a perspective view of freeze sensor  120  according to an alternate embodiment of the present invention. The functions of LEDs  18 ,  22 ,  24 , and  26 , and the function of air holes  32  are the same as those described for  FIG. 2 . The switching between the ‘test’ and ‘service’ modes is now activated by commands from a remote system. 
   Referring now to  FIG. 7 , a flow chart depicting the internal logic periodically evaluated by MCU  10  of freeze sensor  120 , according to an alternate embodiment of the present invention. The difference between the logic of the preferred embodiment shown in  FIG. 4  and that of an alternative embodiment shown in  FIG. 7  lays in the method of ensuring reliability of communication between the present invention and the remote system. The preferred embodiment transmits the signal multiple times to increase the chances that the remote system will receive the signal; the alternate embodiment expects a confirmation message from the remote system and re-transmits the signal until a confirmation is received. In particular, referring to  FIG. 7 , operational block  152  and functional block  166  are the only two blocks different from the corresponding ones in  FIG. 4 . When the FREEZE — STATE signal transitions from ‘1’ to ‘0’ or from ‘0’ to ‘1’ as in blocks  62  and  78 , flag CONFIRMED is set to ‘0’ to initialize the confirmation-checking process. When the time elapsed since the last transmission exceeds the transmission interval τ x  as in the case of the positive outcome of operational block  50 , flag CONFIRMED is checked at block  152 . A value of ‘0’ indicates that the expected confirmation has not been received. The program control then continues to “TRANSMIT DATA” at block  68  and update the last transmission time t x  to the current time t, and then the cycle continues anew at block  44 . It should be noted that there is a separate interrupt routine (not shown in  FIG. 7 ) processed by MCU  10  upon an interrupt generated by transceiver  116  when a message is received. The said interrupt routine inspects the received message and sets flag CONFIRMED to ‘1’ if the message confirms receipt by the remote system of a recent freeze state signal transmission. 
   The present invention as described in  FIGS. 1–7 , can be used as a freeze-sensing module for an automated freeze prevention system or for providing an effective and reliable freeze alert to a central monitoring system. As an example illustrating the usage of the present invention in such applications,  FIG. 8  shows that a multiplicity of the preferred embodiment of the present invention  20  are used as sensing modules for an existing alert system  200 . The alert system  200  contains a transceiver  202  for receiving the freeze state signal among other types of signals the alert system is designed for. Transceiver  202  is connected to micro controller  210  that operatively connects with user interface module  204  and alert/alarm module  212 . The user interface module  204  provides means for entering configuration settings including settings for the freeze sensors (such as network ID, unit ID) and for issuing command for operation modes. The alert/alarm module  212  could be a simple audio alarm or capable of dialing a phone number to leave a message or sending an email text message. The EEPROM  206  contains the configuration parameters, device information, and email addresses or phone numbers needed for dispatching the alert message. 
   Referring to  FIG. 9 , shown is a flow chart of logical operations for managing freeze alarm/alert, adaptable into an existing central alert system  200 . Upon receiving a freeze state signal from one of the freeze sensors  20 , micro controller  210  executes the program shown in  FIG. 9 . Generally, the alert system keeps a FREEZE — THREAT — LIST that contains the UIDs of those freeze sensors that have detected a freeze threat condition, i.e., whose FREEZE — STATE has changed from ‘0’ to ‘1’. This list can provide specific location information for the freeze threat condition. When the FREEZE — THREAT — LIST is not empty, the alert system&#39;s FREEZE — ALERT flag is set to ‘ON’, otherwise to ‘OFF’. This flag could be linked to a visual alert such as an LED on the alert system housing, an audio alarm, or a text message sent to predefined destinations. If a freeze sensor reports FREEZE — STATE=1 as in case of the positive response of operational block  220 , the sensor&#39;s UID is added to the FREEZE — THREAT — LIST at block  224  if it is not already in the list. Each time a new freeze threat is detected, control issues a FREEZE — ALERT — ON command (block  226 ) that sets an alarm or sends an alert associated with the specific reporting sensor. On the other hand, each time when a freeze sensor clears its freeze threat state (i.e., FREEZE — STATE changes from ‘1’ to ‘0’), control sends a FREEZE — ALERT — OFF command (block  238 ) that cancels the corresponding alarm or clears the corresponding alert associated with the reporting freeze sensor. 
     FIGS. 10A–10D  are cross-sectioned, elevation views of some typical freeze sensor component embodiments.  FIG. 10A  shows a thermal sensor  300  as the freeze detection sensor according to the preferred embodiment of the present invention. Thermal sensor  300  is connected to a data analysis and control unit  36  that is in turn connected to a transmitter  16 . Air holes  32  in the freeze sensor housing  34  permit thermal sensing of ambient air temperature. 
     FIG. 10B  shows another embodiment, in particular, replacing the thermal sensor  300  of  FIG. 10A  with a pressure sensor  302  attached to a pipe connection fitting  304  in the freeze sensor housing  34 . In this embodiment, water pressure within the attached pipe is sensed by pressure sensor  302  and is passed to the data analysis and control circuit  36  that decides on the freeze state based an evaluation of a logic program. Said logic program is much the same as that shown in  FIG. 4  or  FIG. 7 . 
     FIG. 10C  shows an embodiment where pressure sensor  306  is located outside the freeze sensor housing  34  and is connected to a data analysis and control unit  36  that is in turn connected to a transmitter  16 . Such an arrangement allows existing pressure sensing devices to be upgraded to provide freeze alert functionality. 
     FIG. 10D  shows another embodiment with more than one freeze condition sensor connected to the data analysis and control unit  36 , in this instance, a thermal sensor  300  and pressure sensor  306 . Both sensors are connected to a data analysis and control unit  36  that is in turn connected to a transmitter  16 . 
   To use the present invention in association with an alert system or an automatic freeze prevention system capable of receiving wireless signals, one needs to place one or more freeze sensors developed according to the present invention in locations next to water pipes that are most susceptible to freeze when temperature falls below freezing, especially unheated areas. Up to 16 such freeze sensors can be deployed for each said system. Each freeze sensor in said system should be assigned a unique UID, while all freeze sensors in one system should have the same NID as that of said system. If the temperature stays above the predefined T threat  (usually at around 1° C.), the alert system will not receive any signal from said freeze sensors. Once the temperature drops below the T threat  at the location of one of the sensors, the alert system should receive a freeze threat signal that causes the alert system to set its alarm and/or send an alert message as configured. Once the temperature rises above the T safe  level (usually higher than T threat  by 1–2° C.), the alert system should receive a freeze safe signal that clears the alert associated with the reporting freeze sensor. 
   While the above illustrations and description contain many specifics, these should not be construed as limitations on the scope of the invention, but rather as an exemplification of preferred embodiments thereof. Many other variations are possible. For example, the transmitted freeze state signal does not have to be either 0 or 1 and need not be sent a limited number of times after the freeze state changes. Instead said signal could be derived from some other manipulation, e.g., a proportional operation, on the outputs of the freeze detection sensor ( 2  in  FIG. 1  and  FIG. 5 ), and all samples measured from the time when the temperature drops below T threat  until the time when the temperature rises above T safe  could be transmitted. A particular example is that the transmitted signal is simply the temperature measurements between t threat  and t safe  as in the temporal view of temperature  41  in  FIG. 3 . In such embodiments, the freeze state decision logic programs illustrated in  FIG. 4  and  FIG. 7  and the alert management logic in  FIG. 9  can be easily adapted by those skilled in the art. Further examples of other variations of the described embodiments of the present invention include using dials as interfaces for configuring the NID and UID, or input key pads combined with an LCD display (an expensive option), or remote configuration commands sent from any wireless device or computer that can communicate with the transceiver of the invention.