You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims priority from U.S. provisional patent application entitled “Swimmer Safety Tags”, Ser. No. 60/951,243 filed on Jul. 23, 2007. Said provisional application is incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The present invention is in the field of swimmer safety. 
   COPYRIGHT AND TRADEMARK NOTICE 
   A portion of the disclosure of this patent document contains material to which a claim for copyright is made. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure as it appears in the Patent and Trademark Office patent file or records, but reserves all other copyright rights whatsoever. 
   The word “WAHOOO” and fish logo as shown, inter alia, as item  1116  in  FIG. 11A  are trademarks of Aquatic Safety Concepts LLC. 
   BACKGROUND 
   Drowning is the second leading cause of accidental death in children in the United States. Adults are present in ninety percent of those incidents, intending to monitor the children to prevent drowning, yet the children all too often drown in silence, as their instantaneous peril readily escapes notice. Adult drownings in supervised settings are sadly common for the same reason. 
   SUMMARY OF THE INVENTION 
   The Summary of the Invention is provided as a guide to understanding the invention. It does not necessarily describe the most generic embodiment of the invention or all species of the invention disclosed herein. 
   The systems and methods of the present invention are designed to assist supervisory personnel to monitor people to reduce the risk of dangerous submersions. The invention advances the art by providing effective and commercially economical means to automate prompt notice of supervisory personnel of a person in potential distress. 
   The systems and methods of the present invention comprise equipping each person to be monitored in an aquatic environment with an electronic Tag worn on the body at a position from which immersion of the nose and mouth can be inferred, together with means for timing the immersion of the Tag in water for one or more periods of time associated with possible risk of drowning, and means for communicating between the Tag and electronic monitoring equipment, including alarms, and devices for system control and communications. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a view of the entrance to a pool area where swimmers place Swimmer Safety Tags on their persons. 
       FIG. 2  is a view of swimmers wearing Tags entering the water. 
       FIG. 3  is a view of swimmers being monitored by a Swim Monitor Unit. 
       FIG. 4  is a view of a swimmer setting off a Yellow Alert. 
       FIG. 5  is a view of lifeguard and Control Unit being notified of a Yellow Alert. 
       FIG. 6  is a view of a swimmer setting off a Red Alarm. 
       FIG. 7  is a view of a lifeguard responding to a Red Alarm. 
       FIG. 8  is a view of a lifeguard rescuing a swimmer who triggered a Red Alarm. 
       FIG. 9  is a view of a pool with exemplary hydrophone placement. 
       FIG. 10  is a view of a pool with alternative exemplary hydrophone placement. 
       FIGS. 11A-11D  are views of an exemplary Swimmer Safety Tag (“Tag”). 
       FIG. 12  is an exploded perspective view of a Tag. 
       FIG. 12  is a top view of an alternative Tag design. 
       FIGS. 14A-14D  are cross sectional views of an exemplary means for packaging and dispensing Tags. 
       FIG. 15  is a perspective view of an exemplary means for packaging Tags for retail sale. 
       FIG. 16  is a top view of an alternative exemplary means for packaging Tags for retail sale. 
       FIG. 17  illustrates a method for refurbishing Tags. 
       FIG. 18  illustrates a means for mounting Tags on a swimmer&#39;s head using an elastic band. 
       FIG. 19  illustrates a means for mounting Tags on a swimmer&#39;s head using adhesive “wings”. 
       FIG. 20  is an illustration of an alternative means for determining how long a swimmer&#39;s head has been below water using the blockage of radio transmissions. 
       FIGS. 21A-21C  are illustrations of a hip mounted Tag. 
       FIG. 22  illustrates the functionality of a hip mounted Tag. 
       FIGS. 23A-23C  illustrate an exemplary annunciation unit portion of a Swim Monitor Unit. 
       FIG. 24  illustrates means for recharging the battery of an annunciation unit and alternative means for storing a connecting cable. 
       FIGS. 25A-25B  illustrate an exemplary hydrophone unit portion of a Swim Monitor Unit. 
       FIG. 26  illustrates alternative positioning of an annunciation unit. 
       FIG. 27  illustrates an exemplary Control Unit. 
       FIG. 28  illustrates means for an annunciation unit to communicate with supervisory units as well as the Control Unit. 
       FIG. 29  is an illustration of a neck mounted Tag. 
       FIG. 30  is an illustration of an ear mounted Tag. 
       FIG. 31  is an illustration of a neck mounted Tag. 
       FIG. 32  is an illustration of an alternative ear mounted Tag. 
   

   DETAILED DESCRIPTION 
   The following detailed description discloses various embodiments and features of the invention. These embodiments and features are meant to be exemplary and not limiting. 
   As used herein, the term “about” means within +/−20% of a given value unless specifically indicated otherwise. 
   Method for Increasing the Safety of Swimmers 
     FIGS. 1 to 8  illustrate an exemplary method for increasing the safety of swimmers as applied to a pool area. Similar methods can be applied to open water swimming areas, such a lake or ocean. 
   Referring to  FIG. 1 , a pool area  100  is surrounded by a perimeter fence  120  with an opening  122  therein. Swimmers, such as children  102 , or adults  108 , pass through said opening on their way to the pool area. Each swimmer is provided with a Swimmer Safety Tag  104  that is affixed to a position on his or her head. Suitable positions include the forehead  106  or behind an ear. The Tags are provided with an adhesive so that they will remain affixed even in water, but can be removed without undue force or discomfort. Hence said Tags are said to be “removably mountable”. The adhesive used in water-proof bandages is suitable. 
   The Tags may be stored in a locker  112 . A supervisor  110  may be present to provide assistance with putting a Tag on and/or to make sure that all persons entering the pool area are “Tagged”. 
   Referring to  FIG. 2 , the Tags  202  are electronic devices which will determine, inter alia, how long a person&#39;s head has been underwater and hence, by implication, how long both their nose and mouth are underwater. If a person&#39;s head has been underwater longer than a predetermined safe period, such as 30 seconds, an alarm will be triggered. Different alarm levels may be set at different time periods. A “Yellow Alert” may be set in the range of 20-30 seconds. A “Red Alarm” may be set in the range of 30-45 seconds. A preferred range for Yellow Alerts is 20 to 25 seconds. This will provide adequate warning to a lifeguard to identify, rescue and administer first aid to a distressed swimmer. A 20-25 second delay to Yellow Alert may be particularly suitable for young children, such as those six years old and under. These children would be less likely swim underwater for 25 seconds as part of their normal play the way older or more skilled children can. 
   An alternative alarm is simply a Red Alarm that is triggered by a Tag being underwater for 25 seconds or longer. 
   The Tags are activated when a person&#39;s head  204  enters the water  210 . The alarm signal may be an ultrasonic signal transmitted through the water. 
   Referring to  FIG. 3 , the pool water is monitored by one or more Swim Monitor Units (SMU)  302 . A Swim Monitor Unit comprises an annunciation unit  310 , a connector cable  320  and a hydrophone unit  330 . The annunciation unit may comprise a strobe light  312 . They hydrophone unit may be placed near the bottom of the pool. 
   Referring to  FIG. 4 , the hydrophone unit  430  listens for ultrasonic signals from the Tags. If a swimmer&#39;s head had been below the water for more than the Yellow Alert period, for example, then that swimmer&#39;s Tag gives off the ultrasonic Yellow Alert  402 . The signal is received  404  by the hydrophone unit and is transmitted (e.g. electrically) along the connector cable to the annunciation unit and the annunciation unit takes appropriate action, such as flashing the strobe  412 . 
   Referring to  FIG. 5 , in addition to flashing the strobe, the annunciation unit  502  may also transmit a radio signal  504  to a nearby Supervisory Control Unit  510 . The radio transmission may be at typical frequency bands allocated to alarms, such 433 MHz The Control Unit, in turn, may also take appropriate action, such as flashing its strobe  512  and activating  514  other visual or audio alarms  520 . 
   Alternatively or in addition, the annunciation unit may communicate  506  an alarm signal directly to a portable reception unit  540  worn by a lifeguard  530 . Communication may be via suitable portable unit communications means, such as digital signals utilizing Bluetooth® technology or Bluetooth® Version  2  technology (collectively “Bluetooth” herein). The portable reception unit may notify the life guard that there is an alert via light, noise and/or vibration  542 . 
   Upon activation of a Yellow Alert, a lifeguard may take appropriate action, such as to call for a “buddy check” where all swimmers grab their buddy&#39;s hand and hold it up. This way the lifeguard can quickly confirm and identify which swimmer is in distress. 
   Referring to  FIG. 6 , if a swimmer&#39;s head is underwater for more than the Red Alarm period (e.g. 45 seconds), then the Swimmer Safety Tag may transmit  602  a Red Alarm. The hydrophone will receive the Red Alarm and the annunciation unit and other components of the system may take appropriate action, such as sounding an audio alarm or notifying local emergency medical personnel. The lifeguard, in turn, may take appropriate action, such as clearing the pool of all swimmers and searching for the swimmer in distress. 
   Referring to  FIGS. 7 and 8 , once the swimmer in distress is located, the lifeguard  702  can retrieve the swimmer and apply appropriate first aid if needed. The life guard may also reset the alarm system to the standby state and silence the alarms. 
   In an alternative embodiment, the Red Alarm automatically resets after a certain period of time. 1 to 2 minutes is an appropriate period of time. The benefit of a Red Alarm automatically resetting after 1 to 2 minutes is that by that time, it is likely that a lifeguard is applying first aid to the distressed swimmer. A continuous alarm would otherwise distract the lifeguard during the administration of first aid when the lifeguard must pay particular attention to, for example, the proper administration of artificial respiration. 
   System for Increasing the Safety of Swimmers 
   It will be appreciated by a person of ordinary skill in the art of water safety, that a practical system implementing the methods describe herein must simultaneously meet a number of demanding criteria. These criteria include, but are not limited to:
         Acceptably low number of “false positives”. Similar to the “Boy who Cried Wolf”, If the system constantly indicates that a swimmer is in distress when, in fact, that isn&#39;t the case, then personnel will learn to ignore the system and thus not respond appropriately when a swimmer really is in peril.   Very low number of false negatives. The system must be very reliable in terms of identifying swimmers that really are in distress.   Acceptable to users. The system, and in particular the Swimmer Safety Tags, must be acceptable to the users. Otherwise they will resist using them, their enjoyment will be degraded and their safety compromised. Similarly, the supervisory personnel, such as lifeguards, must find the system easy to use and understand.   Cost effective. The cost of the system must be commensurate with the benefits provided, competitive with alternatives, and encourage its use.   Safe to use. The system should not introduce new safety hazards that negate the overall benefit provided to the users. Similarly, the system should be environmentally compatible.       

     FIGS. 9 and 10  illustrate an embodiment of the present invention that has improved reliability in terms of picking up a swimmer&#39;s ultrasonic distress signal (i.e. lower false negatives). It is common for splashing, bubbles and clusters of swimmers  910  to exist from time to time in a pool. These effects can collectively block a distress signal  912  from reaching a given hydrophone  902 . With at least a second hydrophone  904  mounted in the pool, the probability of a distress signal  914  reaching at least one unit is significantly increased. Suitable positioning of four hydrophones  1002  is illustrated in  FIG. 10 . 
   Referring back to  FIG. 9 , in addition to normal duties, a lifeguard  920  may be responsible for observing all swimmers and insisting that any swimmer  930  without a Tag either get a Tag or leave the pool area. This task can be facilitated by providing Tags with a light so that they can be more easily seen. 
     FIGS. 11A-11  D illustrate embodiments of the Tags that have improved user acceptability and reduced numbers of false positives.  FIG. 11A  illustrates a top perspective view of a Tag;  FIG. 11B  illustrates a bottom perspective view of a Tag;  FIG. 11C  illustrates the size scale of a Tag; and  FIG. 11D  illustrates the mounting of a Tag on a swimmer. 
   Referring to  FIGS. 11A and 11C , a Tag  1100  may have a diameter  1112  in the range of 5 to 30 mm, and a thickness  1114  in the range of 1 to 10 mm. A preferred range for diameters is 10 to 20 mm. A preferred range of thicknesses is 3 to 5 mm. These dimensions give the Tag a size, shape and heft (i.e. perceived weight in the hand) comparable to that of common coins (e.g. US pennies, dimes, nickels and quarters  1130 ). An exemplary Tag, for example, would have a diameter of 20 mm, a thickness of 5 mm and a weight of 3 gm in air. The maximum suitable weight would be 10 gm in air. Thus mounting a Tag on a swimmer&#39;s head ( FIG. 11D ) would not be perceived as an undue burden. Furthermore, Tags could be effectively manipulated by persons of ordinary physical skill and dexterity. Supervisory personnel could place Tags on persons with physical handicaps. 
   The top surface of a Tag could be provided with a logo  1116  or other suitable indicia such as a decoration (e.g. flower) or affinity brand (e.g. sports logo). A light source, such as an LED  1118 , can be provided for easy identification as well as providing an indication that the Tag is functioning properly. The LED may blink at a frequency of no less than once every 10 seconds. This will help conserve battery life. The Tag may also be programmed to flash the LED or multiple LEDs very brightly or frequently in the event of a Yellow or Red Alarm. This will help a lifeguard identify which swimmer is in distress. The LEDs may also change color in response to a Yellow or Red Alarm. 
   Electrical contacts  1110  may be provided on opposite sides of a Tag to sense immersion in water. The water acts as a conductor and closes a circuit between the contacts when the Tag is immersed. An internal timer then initiates. If the Tag is removed from water, the circuit is open and the timer stops and resets. 
   Referring to  FIG. 11B , an adhesive  1112  may be provided on the bottom of a Tag. The adhesive should be medical grade, hypo-allergenic and non-irritating. It should be able to adhere the Tag to a swimmer&#39;s head for not less than 10 hours. 
   A sensor  1114  may also be provided on the bottom of the Tag to confirm that the Tag is mounted on a person. The sensor may be an optical switch that opens when illuminated. Thus when the Tag is mounted on a person, the switch is dark and closed and the internal circuitry functions normally. If the Tag is removed or falls off, then the switch is illuminated and opens. The Tag may either then stop functioning, or may issue a signal indicating that it is no longer mounted on a person. If the Tag is made more dense than water, it will sink and can be retrieved by a vacuum. If a Tag is less dense than water, it will float and can be retrieved by skimming. 
   An alternative sensor is one that optically measures oxygen in the blood directly below the Tag. This can be used to confirm mounting on the person as well as provide an alternative measure of the distress of a person. If the oxygen is low, then the person is in distress. Similarly, the pulse can be measured and interpreted accordingly. 
   Another alternative sensor comprises a pair of electrical contacts  1117  on the bottom of a Tag. They are normally dry as long as the Tag is mounted on a person. If the Tag falls off in the water, however, then the contacts are connected electrically through the conductivity of the water and the Tag has an indication that it is no longer mounted on a person. 
     FIG. 12  illustrates an exploded perspective view of the Tag of  FIGS. 11A-11D . The Tag  1200  comprises a top encapsulating layer  1210 , a battery  1220 , electronic circuitry  1230 , a piezoelectric transducer  1240 , a bottom encapsulating layer  1250  and an adhesive layer  1260 . 
   The top encapsulating layer may be a waterproof, two-part epoxy designed to protect electronics that are submerged in water. The Tag should be water proof to a depth of 300 meters. The epoxy may be cast over the electronics and underneath and allowed to harden. Alternatively, the top encapsulating layer may be a cover that is bonded to the bottom encapsulating layer. 
   Openings  1214  may be milled in the top encapsulating layer after it hardens to expose electrical contacts  1232  on the circuit board of the electronic circuitry. This would allow the circuit between the electrical contacts to close when the Tag was immersed in water and thus begin a timer. Alternatively, a conductor  1212  may pass through the top of the encapsulating layer as one contact, and one or more opening  1252  may be milled in the bottom encapsulating layer to expose the piezoelectric layer. The piezoelectric layer, therefore, acts as the second contact. The circuit between the top conductor and piezoelectric layer then is closed when the Tag is immersed in water. Four openings  1252  may be milled at four compass points to reduce the chance that a swimmer&#39;s skin blocks all of the openings to the piezoelectric contact. 
   Both the electrical circuit components and programming logic are chosen to give reliable performance with minimized power draw. This improves the reliability and lifetime of the Tag. The Tag may have an operating lifetime of at least 30 days, and a storage shelf-life of at least 2 years. The Tag may further comprise an activation means, such as a pull tab, which turns the Tag on. 
   The electrical circuit comprises a micro processor  1234 , amplifier  1238  and optional LED  1239 . 
   A suitable micro processor is a PIC10F220, 6 pin, 8 bit flash microcontroller by Microchip Technology Inc. Said microprocessor is more fully described in PIC10F220/22 Data Sheet, publication number DS41270A by Microchip Technology Inc, 2005. Said publication is incorporated herein by reference. Other microprocessors with similar performance, power draws, cost and size characteristics may also be suitable. 
   The microprocessor may be programmed to have different outputs in different states. The states and outputs are presented in Table 1. 
   
     
       
             
             
             
           
         
             
               TABLE 1 
             
             
                 
             
             
                 
                 
               Duty Cycle 
             
             
                 
                 
               (Duration per 1.1 or 
             
             
               State 
               Output 
               2.2 second cycles) 
             
             
                 
             
           
           
             
               Resting 
               71.4 kHz square wave 
                15 ms 
             
             
                 
               (ultrasonic) 
             
             
               Yellow Alert 
               71.4 kHz square wave 
               300 ms 
             
             
               Red Alarm 
               71.4 kHz square wave 
               700 ms 
             
             
               Low battery (&lt;20% 
                1.2 kHz square wave 
               750 ms 
             
             
               remaining power) or 
               (audible) 
             
             
               detached Tag 
             
             
                 
             
           
        
       
     
   
   The output of the microprocessor is amplified by the amplifier and then used to drive the piezoelectric layer to give the ultrasonic or audible signal. An inductor may be placed in series with the piezoelectric layer. The inductance is selected based on the effective capacitance of the piezoelectric layer to give a resonance frequency of the circuit about that of the desired ultrasonic frequency. This improves the power efficiency of the circuit. 
   A suitable piezoelectric layer is a CEB-20D64 piezoelectric diaphragm made by CUI Inc. The technical specifications of said diaphragm are described more fully in the CUI spec sheet for the CEB-20D64 dated Jul. 28, 2006. Said spec sheet is incorporated herein by reference. This diaphragm is disk shaped and has a suitable diameter (20 mm), material of construction (brass) and cost ($0.75 ea) for this application. It is surprising that it provides adequate ultrasonic emissions, however, given that the mechanical resonance frequency is 6.5+/−0.5 KHz. 
   The resting state is the normal default state of the system. The microprocessor is normally in a very low current “sleep” mode. Every 1.1 or 2.2 seconds (selectable by the user), it “wakes up” and determines the state that it is in. If the clock timer indicating submersion is less than the Yellow Alert level (e.g. less than 30 seconds) then it gives a 15 ms ultrasonic “ping” at 71.4 kHz. Ultrasonic frequencies in the range of 30 kHz to 100 kHz may also be used. At lower frequencies, naturally occurring ambient noise causes interferences. At higher frequencies, more expensive and different shaped (e.g. cylindrical) ultrasonic transducers must be used. 71.4 kHz was selected in this particular application since it represents an even multiple of the clock speed of the microprocessor. Thus, generating the square wave comprises counting clock cycles. It also gives a wavelength of the ultrasonic transmissions in water of about 2 cm. This wavelength is suitable in pools. Longer wavelengths, such as 10 cm, can lead to “dead spots” in the pool where the emitted ultrasonic waves destructively interfere with each other might not be heard by a hydrophone if said hydrophone were located in said dead spot. 
   The ping can be received by the hydrophones and might serve, for example, for counting the number of swimmers in the water in any given time. Ideally the ping should be as short as possible to minimize resting state power draw on the battery. Ping durations in the range of 5 ms to 30 ms are acceptable. The ping should have a large enough amplitude or power so that it is detectible by a hydrophone no less than 50 meters away. 
   If the microprocessor wakes up and determines that the submersion timer has exceeded the Yellow Alert level, then it gives a Yellow Alert signal of 300 ms at 71.4 kHz. This is immediately picked up by one or more hydrophones and a Yellow Alert is initiated. The nearest hydrophone to the signal may have an appropriate indication to assist the lifeguard in locating the distressed swimmer. The microprocessor may also simultaneously drive the piezoelectric layer to emit a loud sonic signal. This will help a lifeguard identify which swimmer is in distress. 
   If the microprocessor determines that the submersion timer has exceeded the Red Alarm level, then a Red Alarm signal of 700 ms is given. The hydrophones then react accordingly. 
   The relative and absolute length and frequency of the Yellow Alert and Red Alarm signals can be varied so long as they are readily discriminated by the hydrophones. An advantage of selecting a Red Alarm duration that is more than twice the duration of a Yellow Alert signal is that the system can discriminate between two simultaneous Yellow Alerts and a single Red Alarm. An advantage of having a pause between Red Alarm signals is that the system can discriminate between a single Red Alarm signal and multiple Red+Red or Red+Yellow signals. Multiple Red+Red or Red+Yellow signals would indicate that more than one swimmer was at risk. 
   An advantage of having each tag broadcast a similar signal is that the Yellow Alert or Red Alarm message will get through even if there is significant echoing within the pool. 
   The system can be designed to provide digital information encoded in the ultrasonic carrier wave. This has the advantage of being able to directly identify which tag is emitting a distress signal. 
   The low battery and/or detached Tag signal can be initiated when the battery voltage indicates that less than 20% of the battery life is remaining or when a sensor indicating that a Tag is immersed but not attached to a swimmer is indicated. The signal can be an audible 1.2 kHz signal pulsed for 750 ms per cycle. 0.5 to 2.0 kHz are also acceptable. The audible signal has the advantage of making it readily apparent to persons nearby that a Tag has a low battery or is off of a person. 
   A suitable battery is a CR1616 2, 3V, Lithium Coin Cell battery made by Panasonic. The technical specifications of these batteries are described more fully in the Panasonic Lithium Handbook, August 2005. Said handbook is incorporated herein by reference. The batteries are rechargeable, have a size that is suitable for this application and have a power rating of 50 milliamp hours at 3V when fully charged. A power rating of 25 to 74 milliamp-hours is suitable in this application. 
   The above described system has a current draw of 2 micro amps when it is in storage. That gives an estimated battery shelf life of about 3 years. The Resting state current draw is 65 micro amps. That corresponds to a 30 day life of submersions. There is enough power to give a Red Alarm for 16 hours. The low battery signal will last 8 days. 
   The order of the layers in  FIG. 12  can be varied. The battery, for example, can be below the electronic circuit. 
     FIG. 13  shows a top view of an alternative Tag design  1300  for detecting submersion. The circuitry is sealed within a water tight enclosure  1306 . Electrical contacts  1304  protrude into a porous protective enclosure  1302 . When water penetrates the enclosure, the circuit is closed. 
   Packaging of Tags 
     FIGS. 14A-14D  illustrate cross sections of a suitable packaging method for the Tags. 
   Referring to  FIG. 14  A, a packaging card  1410  comprises a substrate layer  1412 , and adhesive layer  1414  and a backing layer  1416 . The substrate and backing layers may be made of cardboard. The adhesive layer may be a double stick tape with hypoallergenic, waterproof bandage adhesive. A round opening  1418  is provided to receive a Tag  1400 . The Tag has rounded edges  1401  to facilitate handling. The opening may comprise a protective bumper  1420 . The Tag is pressed onto the exposed adhesive layer  1406  which, in turn, is backed by a disk  1402 . The disk is made of a material that the adhesive does not stick well to. 
     FIG. 14B  shows how the assembly looks for shipping. 
     FIG. 14C  shows how a Tab would be pushed out of the packaging card by an end user. 
     FIG. 14D  shows how the backing disk would be removed leaving behind the adhesive layer  1406 . 
   The adhesive should stick more strongly to the Tab than it would to a person&#39;s skin so that the adhesive is removed from said person&#39;s skin when the Tab is removed. 
     FIG. 15  shows how a packaging card  1506  would be incorporated into a commercial retail package  1500 . Wings  1508  may be attached to the packaging card with appropriate information and indicia printed thereupon. The assembly may be folded  1504  and inserted into a sleeve  1502 . 
     FIG. 16  illustrates alternative packaging for a single Tag  1604 . The single Tag is packaged in a hinged container  1602  and the hinged container is mounted on a retailing card  1600 . 
   Refurbishing Tags 
   The Tags may be recycled.  FIG. 17  illustrates a suitable refurbishing process. Used Tags are collected  1702  and shipped  1704  to a refurbishing facility  1706 . The Tags are cleaned, tested  1708 , recharged  1710 , and inspected  1712 . New adhesive  1715  is applied  1714  to the Tags  1713  and the Tags are packaged  1716 , crated  1718  and shipped  1720  to an end user  1722 . 
   Alternative Tag Technologies 
     FIG. 18  illustrates an alternative mounting technology for a Tag. The Tag  1802  is provides with an adjustable elastic strap  1804 . The assembly  1800  is then worn around the head of a swimmer. 
     FIGS. 19A to 19D  illustrates an adhesive bandage type of mounting. A Tag  1900  is provided with flexible adhesive wings  1902 . The assembly is then adhered to the head of a swimmer.  FIG. 19A  shows a top view;  FIG. 19B  shows a side view;  FIG. 19C  shows a size comparison with a US quarter; and  FIG. 19D  shows the Tag mounted on a swimmer&#39;s head. 
   This configuration has the advantage of providing a convenient means for mounting a radio antenna  1904  on a Tag. The antenna facilitates an alternative means for determining how long a person&#39;s head has been underwater. 
     FIG. 20  shows a radio means for determining how long a person&#39;s head has been in water. A swimmer  2002  has a Tag mounted on his or her head. The Tag emits a constant or pulsed radio signal  2004 , along with identifying information to a control station  2006 . The control station keeps track of all Tags. When a person goes swimming and their head goes below water, the signal is blocked  2012  by water. The control station determines that a particular Tag is no longer above water and a timer  2008  is started. If the timer reaches a certain threshold, then a Yellow Alert or a Red Alarm may be signaled. 
   This system is advantageous at beaches where large distances can separate swimmers and where mounting and positioning of sonar based Swim Monitor Units may be difficult. 
     FIGS. 21A-21C  illustrate a hip mounted Tag design  2100 .  FIG. 21A  shows a top view;  FIG. 21B  shows a bottom view; and  FIG. 21C  shows a perspective view with a size comparison to a US quarter  2110 . 
   This Tag is larger than the coin size sonar based Tag discussed with reference to  FIG. 11C . The size may be 6 cm ( 2102 ) by 7 cm ( 2104 ). The maximum dimension may be 10 cm. The corners may be rounded  2106  to avoid snagging on clothes. The larger size facilitates the incorporation of larger indicia  2108  and strobe lights  2112 . Mounting means, such as a safety pin  2114  may be provided to removably attach the Tag to clothes and a pressure sensor  2116  may be provided. 
     FIG. 22  shows how a hip mounted Tag would work. The Tag  2206  is mounted on a swimmer  2202 . When the swimmer&#39;s hips are more than one meter  2204  below the surface of the water, a sensor of depth, such as a water pressure sensor, triggers a timer. If the timer runs for the duration of a Yellow Alert or a Red Alarm, the Tag sends a sonar signal to a Swim Monitor Unit. They system is functional for both tall persons and short persons  2208 . 
   Skipping ahead to  FIG. 29 ,  FIG. 29  illustrates a Tag  2900  mounted on a necklace  2910 . The Tag comprises a magnetic latch or mechanical latch  2904  to allow it to be easily put on and removed. The Tag may comprise a water emersion sensor and/or a water depth sensor. The Tag may, for example be set to sound an alarm when the depth is more than 30 cm for a given period of time. 
     FIG. 30  illustrates a Tag  3000  that can be mounted on a swimmer&#39;s ear  3020 . The Tag comprises a sensing unit  3002  and a band  3012 . The sensing unit may comprise electrical contacts  3004  for sensing immersion in water and/or a pressure sensor for detecting immersion at depths greater than a predetermined amount, such as 30 cm. The sensing unit may also comprise LEDs  3006 . 
   The band  3012  may comprise a cushion  3014  as well as a means  3016  to adjust the length. 
   A similar Tag without the band may also be mounted in the hollow  3022  behind a swimmer&#39;s ear by using a moldable waxy mounting compound. 
     FIG. 31  illustrates a Tag  3100  that is in the form of a stiff but flexible open neck band. The Tag comprises a strap  3102  and pads  3104 . The electronics of the Tag can be built into the strap. Electrical contacts  3106  are built in to each end of the strap. Thus, both sides of a swimmers head must be underwater to start the submersion timer. The strap is stiff enough to hold the band onto a swimmer&#39;s head  3110 , but flexible enough to be removed by a person of ordinary strength. The Tag may further comprise one or more LEDs  3108 . 
     FIG. 32  illustrates a Tag  3200  that is mounted on an ear plug. The electronics  3202  are mounted on an elastomeric (e.g. silicone rubber) ear plug  3204  to form a final assembly  3206 . This is then mounted in a swimmer&#39;s ear  3210 . The ear plug may be disposable and the mounting may be mechanical by, for example, a lip (not shown) built into the plug. 
   Swim Monitor Unit 
   Referring back to  FIG. 23 , a swim monitor unit comprises an annunciation unit, connector cable and hydrophone unit.  FIGS. 23A ,  23 B and  23 C illustrate a side, top, and bottom view of an exemplary annunciation unit  2300 . Referring to  FIG. 23A , the annunciation unit comprises a strobe light  2302  for indicating alarm status, a connector cable  2304  for connecting to the submerged hydrophone, and associated electronics  2306  for amplifying and processing the ultrasonic signals received from the Tags. 
   Referring to  FIG. 23B , the annunciation unit further comprises a removable rechargeable battery  2312 , and an LED  2314 , to indicate that it is working. 
   Referring to  FIG. 23C , the annunciation unit further comprises mounting means  2322 , a locking cover  2324  and indicia  2326  indicating product information. 
     FIG. 24  illustrates other features of an annunciation unit  2400 . The rechargeable battery  2402  is removable and may be placed in a recharger  2404  to recharge. The connector cable may be stored in a retractable reel  2406  or expandable coil  2408 . 
     FIGS. 25A-25B  illustrate an exemplary hydrophone unit.  FIG. 25A  shows a perspective top view of the hydrophone unit  2500 ; and  FIG. 25B  shows a side view of the hydrophone unit. 
   Referring to  FIG. 25B , the hydrophone unit comprises a hydrophone  2512  for receiving ultrasonic signals from Tags; a protective cage  2514  to protect the hydrophone unit from, inter alia, swimmers hands and feet, a retractable coil  2516  for storing excess connector cable, and mounting means, such as suction cups  2518  for adhering the hydrophone unit to the wall of a pool. 
   Suitable hydrophone units, such as an SUR-1 Submersible Ultrasonic Receiver, may be obtained from Sonotronics Inc. of Tucson Ariz. The SUR-1 is more fully described on web page “SUR-1 Submersible Ultrasonic Receiver”, www.sonotronics.com/html/products/receivers/sur.html. Said web page is incorporated herein by reference. 
   Suitable hydrophone units may have a bandpass of +/−6 kHz of the designed ultrasonic signal of the Tags. Thus if the Tags are designed to broadcast at about 70 kHz (e.g. 71.4 kHz), then the hydrophone would have a bandpass of 64 to 76 kHz. This relatively narrow bandpass helps filter out background noise. 
     FIG. 26  illustrates alternative mounting configurations for an annunciation unit. The annunciation unit may be mounted horizontally  2602  on the side of the pool. This has the advantage of having the strobe light entirely out of the water. Alternatively, the annunciation unit may be mounted vertically  2602  on the wall of the pool. This has the advantage of providing strobe light to the occupants of the pool that may be underwater at the time of an alarm. Alternatively, the annunciation unit may be mounted on the deck of the pool  2606 . This has the advantage of being relatively easy to install. 
   Supervisory Control Unit 
     FIG. 27  illustrates a face view of an exemplary Supervisory Control Unit  2700 . The control unit comprises a power supply and electronics suitable for receiving signals from annunciation units and transmitting signals to alarms if necessary. The control unit further comprises a locking cover  2702 , indicator LED  2704 , strobe alarm light  2706 , informational screen  2708  and touchpad  2712  for entering data and commands. A US quarter and Tags  2720  are shown to indicate scale. 
   Portable Reception Units 
     FIG. 28  illustrates a number of alternative embodiments of portable reception units that may be worn by a lifeguard or other supervisory personnel. These include ear pieces  2826 , bracelets  2828  and necklace tokens  2832 . These designs may be both functional and have a certain aesthetic appeal. 
   As discussed above, the portable reception units would receive alarms  2824  from annunciation units  2812  after said alarms were received from Tags  2802  worn by swimmers. Communications may be by Bluetooth protocol. 
   Portable Family Systems 
   A completely portable embodiment is suitable for families visiting a body of water. It can consist of Tags, one or more portable battery powered SMU units, a battery powered Supervisory Control Unit and/or one or more Portable Reception Units. The Supervisory Control Unit may be configured like a briefcase or “boom box.” 
   EXAMPLES 
   Example 1 
   A 25 meter long by 6 meter wide indoor pool was equipped with a swim monitor unit. The pool had a shallow end 1 meter in depth, and a deep end 3 meters in depth. The swim monitor unit was mounted at the middle of the wall of the deep end. The hydrophone rested on the bottom of the pool at a depth of 3 meters. The annunciation unit rested on the edge of the wall of the pool and communicated with a Supervisory Control Unit by radio transmission. The supervisory control unit was 3 meters from the annunciation unit. 
   A test swimmer entered the water at the midpoint of the pool and submersed a Tag in the water. The Tag was programmed to emit an ultrasonic Yellow Alert signal at 30 seconds and an ultrasonic Red Alarm signal at 45 seconds. After the Tag had been submersed for 30 seconds, the supervisory control unit sounded a Yellow Alert. The test swimmer then removed the Tag from the water and the Yellow Alert ceased. 
   The test swimmer then put the Tag in the water again. At 30 seconds, the Yellow Alert sounded. At 45 seconds the Red Alarm sounded. The test swimmer removed the Tag from the water and a supervisory person reset the control unit to silence the Red Alarm. 
   10 “interference swimmers” then entered the deep end of the pool, clung to the side walls of the pool and kicked the surface of the water vigorously to produce both bubbles and splashes. The interference swimmers were located between the test swimmer and the swim monitor unit. The test swimmer placed the Tag below the water, but at 30 seconds, no Yellow Alert sounded. The interference swimmers then stopped kicking and the Yellow Alert sounded. 
   A second swim monitor unit was then placed at the midpoint of the wall of the shallow end of the pool behind the test swimmer. The hydrophone was placed on the bottom of the pool at 1 meter depth. The annunciation unit was placed on the wall of the pool. The annunciation unit was about 28 meters from the control unit. 
   There were no interference swimmers between the test swimmer and the shallow end hydrophone. The interference swimmers then began kicking in the deep end and the test swimmer again placed the Tag below the surface of the water. A Yellow Alert sounded after the Tag had been submersed for 30 seconds. 
   Example 2 
   11 swimmers were equipped with Tags placed on their heads. The Tags were 20 mm in diameter, 5 mm thick and weighed about 3.3 gm each. Some Tags were mounted directly onto swimmers&#39; heads using a removable waterproof medical-grade adhesive. They were positioned either on a forehead or behind an ear. Other Tags were mounted on swim goggles or held onto a forehead by an elastic band. The swimmers included children, teenagers and adults of both genders. The swimmers engaged in normal water activities at their own discretion for thirty minutes. All of the Tags stayed on the swimmers. None of swimmers expressed any discomfort with the Tags or expressed a desire to remove a Tag. The only unintentional Yellow Alert that sounded was when an adult swimmer with a Tag mounted behind her ear was resting against the side of the pool with her head inclined back. She was readily identified when the Yellow Alert sounded. 
   CONCLUSION 
   While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. Any of the aspects of the invention of the present invention found to offer advantages over the state of the art may be used separately or in any suitable combination to achieve some or all of the benefits of the invention disclosed herein.

Summary:
Electronic Tags are mounted on swimmers to reduce their risk of drowning by identifying when their heads are underwater for periods of time which may indicate a dangerous submersion situation, and for triggering corresponding alerts and alarms. In this method, each monitored person is equipped with a lightweight electronic Tag worn on the body that communicates with monitors that issue the alerts and alarms, including audible and visible distress signals. The monitors, in turn, communicate the alarms to receivers used by supervisory personnel, such as lifeguards or parents. The invention may be used in aquatic environments, such as public recreation facilities, pools, waterfronts, and water parks, as well as in more private settings, such as homes, apartment buildings or hotels.