CA2054532A1

CA2054532A1 - Life-saving alarm for persons in a water medium

Info

Publication number: CA2054532A1
Application number: CA002054532A
Authority: CA
Inventors: Alfredo T. D. Valdez
Original assignee: Individual
Current assignee: Individual
Priority date: 1990-11-01
Filing date: 1991-10-30
Publication date: 1992-05-02
Also published as: EP0484184A1; MX9101863A; ZA918658B; BR9104729A; JPH04274598A; KR920010521A

Abstract

ABSTRACT OF THE DISCLOSURE

An alarm system for detecting persons who accidentally fall into the water and who are eventually in the water in an emergency situation that requires help, of the kind comprising a signal transmitter means including an activating means for actuating said transmitter means which is sensitive to a pre-determined condition, said transmitter means being attached to the body of the user by removable means of attach-ment, and, at least, a receiver means for receiving said signal and capable of identifying the signal and controlling an alarm device disposed at a place where help is needed.

Description

2 ~;,3 This invention refers to a .~arety system, and more particularly, to a li rc - saving a I ;l 1'111 I~or pcrsol-s in a water medium.
~ ven morc palticularly, il is one objc~t of this invention to provicle an immersion alarm (or an immersion sensor) intended to save thc life of pcrsons, eit]ler children or invalids who accidentally fall into the water, alld even persons practising water sports or swimmers in an emergency situation.
The invention refers to a protective elemcnt to be used mainly by those persons W}10 are not able to swim in case they fall into the water by accident or are totally or partially unable to make thc minimum nccessary movcllle]lts to keep floating.
At the same time, the said protective element allows these persons to be in the watcr plavin or amusinF themselves without anv risk to their lives. Likewise, said element can be used by persons who, even when they can swim, can find themselves in a dangerous situation (cramps, tireness, water-stream pulling, injury, etc.).
In brief, the above-referred invention comprises an alarm means attached to the body of the user in the form of a necklace, belt, wrist strap, ctc. Said alarm means is activated when in contact with water, an~ said c;rcumstance -together with alternatives hereinafter refcrred to- callscs a signal to be emitted.
The inyention is completed Wit]l at least an apparatus .
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2~J~ ~32 2.-receiving said signa]., ~ihicll should bc located with:in a suitablesensing range, so that, wllen tl-e reccivcr senses said signal, it means that the immcrsion in ~Yater o~ tl~e person equipped Wit]l the alar~ eans ll~s bcen ~Ictectc~ d, consc~luelltly, an alert is given on tllis emergency s:ituation. In such case, the receiver in turn activates a SOUlld (or other)alarm device located at a place where help can be g:iven to the person in emergency.
It can also be stated tllat the presence of children at the seaside, or in rivers, ponds, as well as in swimmin-pools or any other water medium, has al~ays been a source of constant worry ancl anxicty to tl~eir l-alellts, cons:icleri.llg tlle large number of deaths ancl accidents related to asphyxia by immersion, especially affecting all ch:ilclrc?n who cannot sw.im.
Regarding the use of electronic media to detect and prevent acuatic accidents produced by asphyxia by immersion, even if there are some antecedents, up to now they have given poor results. ~hy? Because the scarce systems developed until present time, have not succeeded in solving, as yet, aspects of fundamental importance for an efrective safeguard of the physical integrity of persons.
Tllis is mainly due to tlle l~act tha-t thc methods or elements used lack three basic requiremellts: reliability, practicity and simple installat:ion. I~or said reason, the use of the same has not attained d:ir~usion or thc samc have failed, since all. existing apparatus cleserve SCIiOUs object:iolls.

s z Such is the case Or a patent registered more than seventeen years ago, which was unsucces-;rul, precisely due to its signi~icant technical and structural de~iciencies. We specifically rcfer to tlle "Licb" patcn~ tl~at, in its practical implementation, encountered defects J whlch could really not be overcome.
We shall below mention the main objections we find against the "Lieb" patent:
1. It is inspired in the emission of ultrasonic signals or waves, and on account of said signals being extremely directional, the transmitter, supposedly placed on the chest of the user, should be directcd to or "~limillg't directly towards the receiver installed somewhere in the poo~. Conse-quently, it appears absurd to think that a person who is drowning will keep still in the water during the emergency and that, simultaneously, his signal transmitting apparatus will be exactly "aiming" at the element meant for receiving the slgnal.
2. So that the ultrasonic signal transmitter described in the "Lieb" patent had the power and range necessary fo fulfill its functions in a pool of ordinary size, as for instance a pool of 4 m x 5 m, it should have an ultrasonic transducer and batteries of big size. In order to realize the lack of practi-.i~,; .
city or the non-viability of tl-e "Lieb" patent in this respect, we should imagine a child, equipped with a transmitter with .

~0~3~32 4.-the described elements: it would be something so bulky and soheavy, as if }lC carrie~d, hanging ~rom llis l-eck, an al~paratus similar to the battery of a car.

3. The "Lieb" patent is restricted, c~clusively, ror use in swimming pools. That is, it has not been mean~ for use in the sea, rivers, lakes or any other water medium.
To date, such accidents were mostly preveJlted by a simple permanent visual control on small children, which, obviously constitutes a highly unsafe l~recaution.
On the other hand, in crowded places of acuatic amusement and entertainment, an additional control is usually implemented by means Or lifc~llald~ OWCVCI~ since such control is also a visual one, it is as unsafe and subject to failure as the previous one.
Another widely implemented alternative has been that comprising the use of life-jackets or belts. I-~owever, children usually refuse to wear them as said life-saving devices limit their movements and, in addition, they are rather uncomfortable when wet. For said reason, children often take off said life-jackets or belts without their parents noticing said circumstance, and thus remaining w]lolly unprotected.
~ or the particular case Or swimmillg-pools -and the prevention of accidents by immersion therein-, there are other methods which have not been yet referred to but whic}l shall be described hereinafter so as to show disadvantages involved 2 ~

by their use. Such methocls include pelimetral fences, a certain kind of protecting ences, as well as se-veral kinds of coverings or nets. Set forth below are only some of the drawbacks found in such arrangements:
~a) Lt is for children a real amuselllent or "aclventure" to climb or overcome such obstacles.
(b) Children can pass over such fences with the uncautious ~` cooperation of other children.
~c) ~y careleness or negligence of a user, the door on the fence for accessing the pool can be left open.
(d) People coming in or out of the l~ater can get injured ; -as being bare-footed- when stepping oll the means O r engagement or anchoring of such fences.
: (e) Said protective means tend to cast slladows on the solarium itself and, in addition, they lack any aesthetics.
(f) An annoying discrimination is made between those children `;~ who can remain in the pool and those wllo, for being unable toswim, watch the others play from behind the fence.
It is to be noted that existing prevention systems made it difficult and even impossible to determine if someone c is immersed in the water and urgently needs help in such an emergency. Consecluelltly, it can be s;~ at nolle ol the know methods allow non-swimmers to enjoy their healthy acuatic entertainment or refreshing bath ~ithol~t any fear or risk, either they are in the sea, river, ]akes, pools, etc.

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On the other hand, as it is widely known, death by immersion also aEfects old people all~l even expert swimmcrs in critical situation sucl- as on account of cramps, water stream pulling, physical tireness, etc., accidents which can not only accur in seas and rivers but also in lakes and swimming-pools. Think only o the number of lives that could have been saved, should said people have been able to receive immediate assistance in the emergency.
As a result, the invention described in this specification provides an ingenious and effective solution to the above referred problems and allows the presence of children near seas, riversg ponds, swimming-pools or any wa-ter medium, all that without any annoying discrimination and noticeably decreasing the risks of any accidents caused by asphyxia by immersion.
Therefore, the invention herein contained solves the above referred difficulties, on the basis of an alarm means which, once attached to the body of the user (e.g. a child~, either in the form of a necklace, belt, etc. allows parents to be on the alert as soon as the child enters the water, or either, if desired, the child is allowed to remain in the water as long as immcrsion ~ocs l-ot cxcecd thc ncck.
Furthermore, and as above indicated, in the case of swimmers facing critical situations as above indic.lted, they can press a switch to activ~te the alarm.

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' Said alarm means consists o r an immcrsion sensor connected to a transmitter of a remote s;gnal which~ through distance and when said sensor comes in~o contact with water, emits a signal activating the alarm. Illus, it is possible to immediately know when the person to l~hoJn the ~evice llas been attached to has entered the water or h15 accidental]y allen thereinto, and also to have enough time to take the necessary steps to save said person ~either in the sea, river, swimming-pool, etc.).
For the case of an elderly person or a swimmer in emergency, the system is not automatically activated, but by means of a release device, a pusll button, ctc., when necessary.
This invention has also ingeniously solved other troublesonle aspects:
(a) The receiving means (or the transmitter, as desired) .
comprises a device which function is preventing the alarm operation by meTe water splashing or a brief immersion ~only after some seconds the alarm is operated and new warning elements are subsequently activated).
(b) This invention can be used in wide water spaces (sea, river, etc.) without that implying the need of enlarging the size of the rcmotc signal transmitter (i~t is to bc noted that, as being attached to the user's body, said remote signal transmitter should necessarily be small and easy to carry, as well as an aesthetic element).

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~ or the abo~e-reEerred reasons, for use in large water spaces or wide distances, the irlvention additionally comprises a perimetral antenna, one or more buoys, or the arrangement oF posts,piles, rock fills, walls, etc., equipped with Tepeaters, so that the latter reccive the signals from eventual txansmitters and re-transmit the same with greater strength and at longer range.
On the other hand, in highly crowded places (such as beaches or water ~ediums of regular extellt), it is not suficient to receiYe the corresponding signal of alert and so learn that a peTson among the number of people present tfiere is in an emergency situation on account of water immersion.
Then, it becomes mandatory to also deterllline the exact location of said person in the water, so as to immediate help him/her.
T~erefore, the exact location oF the person in danger in highly crowded places is determined by the use oF a monitor or computer lnterface which, by means of radiogonometry or triangulation of buoys or receivers disposed in said posts, piles, rock fills, walIs, etc., accuratelv detects the place where a life shoul~
be saved.
For all the above reasons, it becomes easy to imagine the de~ree o~ accc~tancc this systcm l~i`ll havc OIICC takcn -into , ~ractice, re~ardless of the catePorv or llSC the same maY then haYe, and considering that, on account Or the characteristics defining the same, it can either be usecl by children, old pebple ::
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or invalids, and even by grown-ups and expert swimmers, both in summer resorts ancl in countrics, cl~ s, E.lrms alld weck-cnd houses, including home and, in ~eneral any l~lace in which said ~ersons can acc:idcntally ~all illtO ~llC watcr or be ;n any emergency situation within a water medium which can put his/her life in danger.
For the above described purposes, this invention comprises an alarm system for detecting persons who are accidentally immersed in the water or are eventually in the water in a situation requiring help, W]l:iCh comprises a transmitter means which emits a signal including a means for activating said transmitter mcans whicll :is scnsitivc to a pre-determined condition, said transmitter means being attached to the user's body by removable means of attachment and, at least one receiver means for receiving said signal and capable of identifying said signal and operate an alarm device arranged at the place where help is needed.
Drawings For a better clarity and understanding of the object o this invention, the same is illustrated by means of several figures, in which one preferred :Eorm of embodiment is represented as an example, though not limited thereto, wherein:
Figure 1 is a block di.ll~r.~ ich csse~ lly ~S

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10 . - , shows the circuit forming the liEe-saving device, both regard-ing means for producing the alarm signal and those intendcd to receive and amplify said signal.
Figurc 2 illustratcs the ci ICUit oE the means for transmitting the remote signal.
Figure 3 shows a diagram of the signal receiving circùit.
Figure 4 is a perspective view of an open ring showing the life-saving means both as to the general structure thereof and the arrangement of the different parts and elements forming said means.
Iigure 5 is a vicw of tllc SalllC ring as closed and attached to a child's neck.
Figure 6 is an schematic view of an arrangement whereby the location of the means transmitting the remote signal can be also located within a large water medium.
Figure 7 shows a block diagram of the circuit of another form of embodiment of Figure 6.
Figure 8 shows another form of embodiment which is a plane view of a swimming-pool surrounded by a perimetral antenna, which communicates to a central receiver connected to the alarm means. It is made clear that the use of such perim-etral antenna is advisable only for the case of extraordinarily large swimming pools. For swimming-pools of ordinary dimensions, the power of the transmitter will be surEicient by itself to ~ , ' '' , ~ ' ' .~
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be received by the antenna of the rece:iver.
'1he alarm clcv;.cc Or th;s invclltiotl cssclltia:1ly consists of a transmitter means 20, Or a U111 or Vllll modulated high frequency remote signa], WlliC]I :i]l t~lrJI comprises an activating means 23 for activating saicl transmitter meansl which is carried by the user on a holder elemc7lt 24, The referred system is completed by a receiver means 21 for receiving the signal emitted by the transmitter means 20, w11en activated by the activating means 23, said receiver means 21 being connected to an alarm devi.ce 25 which is operated when the receiver means 21 receives the signal from said transmitter means 20.
Said receiYcr means 21 :is alr.~ cd at a .fixcd placc remote from said transmitter means 20. Said signal tra.nsmitter means 20 as shown in Figure 2 compriscs a 1.:ig11 frequcncy sta~e formed by a high frequency N-P-N transistor TRI connected to the tuned circuit formed bY LI and CVI, CVI bein~ variable in order to fix the frequency.
In series with the collector-emitter path of transistor TRI, there is a resistor RI w}1ich limits the current and is connected to ~round.
Between power supPly and the base of transistor TRI, there is a bias rcsistor R2, and bctwccll sa:i(l tral1sistor basc and the tuned circuit there is a feedback capacitor CI.
The choke ZI connected to tl)c tulled circuit output attenuates the radio frequency flow to thc power supply, and . .
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~0~ 12 -the capacitor CZ limits the radio-requency existing in the emitter of TRI.
1he modulation frequency is received at the base of transistor TRI through diode DI.
The low-frequency stage generating the information to be modulated comprises the integrated circuit ICI which ground-connects the output of contact l7 according to a code established by a combination of groul1d-cor111ecting contacts l to 12 of ICI in a predetermined manner.
In a preferred form of embodiment of this invention, the integrated circuit ICI is ~1~153200N.
During the time in l~hic1~ pulls the DI tension to positive and in consequence the TRI base, the oscillator is deblocked and emits a series of carrier waves during said period.
Contact 13 of ICI constitutes the input of the local oscillator of the integrated circuit, which is connected to the RC~network formed by R3 and C3 and which fixes the clock frequency of the low frequency stage.
The LED diode DLI, further to operating as resist-ance to adjust the feeding tension, is also useful for detecting the correct operation of the signal transmitter, since, wheD
activating mca11s 30 is close~, sets t1lc al1o~le to t]1C sup1ly positiYe tension, and the diode DLI flashes with ti1e power supply i voltage.
Apart from being part of t1~e tuned circuit, coil LI
operate. as transmitting antenna, ~hercby the s1gna1 transm1tter .~ `
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13.-~as highly reduced dimens:ions.
~ lc si.gllal rCCCiV:illg IllCilllS 21 is SllOWIl iJI morc detail in Figure 3, wllicll illustrates ~ circuit diagram thcr~ofthe operation o:L whicll is as hcreinal~cl described.
The signal coming from the antenna ANT is received at the b.ase of txansistor Tl~10 after passing throug}l capacitor C12, both.forming, together with the tuned circuit L10-CV10 and network R10-D10 and R14 the base biasing of transistor TR10, a su~e~leaction type receiYer.
Capacitors C13 and C14 and choke Zl determine the reaction .frequence for detecting thc sigl~
lhis d(tectcd l'C~I s.i.gna:l, OIlCc f.i:ltercd I)y the low-pass filter formed by R13, C15 and C16, whic}l eliminates the h~gh.~requencY component of the signal ~hich lS then amplified b.y~TR12~ which together with low resistance R16 and base polaxization resistance R17, constitutes a hig}l-gain amplifier.
The signal filtered by capacitor C17 is then ampliied by transistor TR13 whic}l is connected to the emitter res.i~tor R21 which limits the capacity o-f the amplifier. Pass-b.and clipping capacitor Cl9 is further connected to the collector and to the base of transistor TR13.
The output ol this amplifyillg stage is coupled with t~e base o.~ transistor TR14, by means ol capacitor C20 and diode D15, once the signal has been dosified by means of diode D12 and filtered by capacitor C21.
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14.-', The following stage comprises a Schmitt trigger,which is formed by transistors ~ and 11~15 and whicll switch-ing threshold is determined by resistor R27.
A square s:igllal is cmitted Erolll the lRl5 receiver, said signal being almost with no deformation and is applied on contact 16 of integrated circuit IC2 to be recognised.
Said PCM signal is compared at IC2 with the shape of the signal which -once previously programmed- is memory-stored and, in case of coincidence, conl1ect to ground contact 17 of IC2.
Once ground-connected, the base oE PNP transistor TRl6, as connected to contact 17 of lC2 by resistor R29, operatesthe transistor and biases the base of transistor TRl7, which is connected to the divider formed by resistors R22 and R32 thus saturating said transistor and activating the coil of relay RLl~ closing contacts C-B and connecting supply to transducer Bo that emits the alarm sound.
The portion of the circuit appearing at the tope is a conventional stabilized continuous current power supply circuit included only as reference for the case in which the circuit is connected to a 12V battery and, therefore, need ` not to be hereln described.
Activating means 23 is formed in this embodiment by two electrodes referred to with numbcr 30 in Figure 2, and ;~; which close the circuit when immersed in water.
~ In order to improve sensiti~ity of the immersion ,.

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sensor, an amplifying stage can be included between electrodes 30 and the circui.t ree(li]lg.
Similarly, a circuit for colltrolling tlle act:ivating means can be includeLl7 W}liC]l allows detcctirlg a temporary closure o-~ the c:ircuit activated by electrodes 30, so as to - avoid the operation of the alarm by tlle mere splash or by onlya brief immersion. Said control circuit is not herein illustrat-ed for being widely known in the art.
The sound alarm device 25 connected to receiver means 21 for receiving tlle remote signa:l, is formed by an acoustic transducer, as referred to as Bo in F:igure 3.
T}lc alarm dcvicc 25 can bc o r l,rogressivc inteJ-Sity.
For the operation o~ tlle alarm system of the present invention, the holder element 24 is attacheLl.to the user, either by the neck, waist or ankle, etc., depending on whether the same is expected to operate whe]l the uscr just enters the water . (ankle~, the water level exceeds a particular limit (waist) or when the water reaches a level of total prohibition or danger (neck~.
ReceiveT means 21 for receiv:ing the remote signal is arranged near the water medium, so tllat when the user carrying tlle rcmotc s:igna] translllittcr Inc.llls 20 c]ltcrs thc water and the acti.vating means Z3 is bclo~ the surface o-f said water meLl:i.um, the samc is activatcd, .lllLl thL respective signal is recelvod by tlle antc~ a, a~ld tl~on alllp:LiLicd, thus ~'' .
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?-activating the alarm device 25 which ;.nd:icates that the useris in the water medium with the act;.vat;ng means Z3 bclow the water sur~acc, said alarm ~evice 25 consc~luently warning the persons in charge of the respective control and surveillance so that they can assist the person in ~In cmergency situation.
In the above-clescribed particular case, as the remote signal transmitter 20 is a Ul-IF or VH~ high-frequency system, a modulation frequency for multiple users can be designed, as consistentwith different kincls of alarms, so that it will be possible to determine which of the users is the one in the water medium with the activatin~ means 23 below the water surface. This is due to the fact that the integrated circuits applied to the signal transmitter means 20 and to the signal receiver means 21 can be programllled.
The form of embodiment illustrated in Figure 8 comprises the possibility of having the antenna of the remote signal receiver means 21 formed by a frame antenna 31 perimetrically disposed with respect to the water medium or pool 32. Such a perimetral antenna allows the reception of the " . remote signal from a very distant place from the site where - the emergency occurs. It is to be noted that the preferred orm of embodiment of this invention is based on the emission of UHF or VHF requency signals.
~; Another form of embodimeTIt Or this alarm system is ill.ustrated in Figure 6 and 7, and allows detecting and . .

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17.-locating a user carryinK the remote signal transmitter means20 when said user is in the water medillln, such as sea, rivcr or lake.
~ igure (~ shows an .Irrangclnc~ y means of which the location o~ tile user carryillg thc rcmote signal transmitter 20 can also be detected, especially when ~le water medium concerned is of great dimensions, such as sea, river, lake, etc.
For this purpose, buoys 33, 34 and 35 are arranged in the water medium 32, said buoys comprising repeater stations which emit signals which are recei-ved ~t the coast 36 by the receiver means 21 having a circuit whicil, in addition to cmitting thc allrln sign;ll, it ;liso ;I~tiv;ltcs thc mollitor Or computer interface 37 in which alarm 33', 34' and 35' is operated according ~o the buoys emitting the signal.
lhe remote signal transmitter means 20, which is attached to the user's body, effects a low-power transmission due to the reduced size thereo~ and its signal is received at a higher degree by the repeater station of the nearestbuoy.
For the case in which the nearer repeater station is one of the bouys 33, 34 and 35, it will re-transmit the signal noticeably increasing its power and range and also at a different frequency.
Figure 7 shows a remote signal transmitter means 20 with an activating means 23 ~hich activates said means, and , . . .

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by means of antenna 42, it transmits thc codified signal which is receive~ by antenna 43 in the nearest huoy having a receiver means 22 similar to that shown in Figure 3.
I`his receiver means 22 is fcd by a feeding battery 45, which is in turn connected to a battery charger 46 for the automatic recharge thereof.
When the receiver means 22 receives the codified signal, the transmitter-repeater 47 is activated, which, in turn, and by means of antenna 48, emits a wider-range signal which is received by antenna 49 of the receiver means 21, this receiver means being connected to the monitor device 37 of Figures 6 and 7 which, by thc soun~l tlalls(lucct and tllc nssociat ed screen, indicates which is the buoy cmitting the signal.
Among the different embodiments of this invention, the holder element 24 for the transmitter means 20 is formed by a band S0 of fixed or adjustable length, which free end includes a closure device formed by a tapered case 52 which in its upper part carries a lug 53 projecting above the upper surface of said case 52, said lug 53 being arranged in a retractile position with respect to case 52 and comprising a locking system by means of a key which can be inserted by opening 54.
The system is complctcd at thc other encl 55 of band 50 by a bridge 56, which allows the passage of case 52 by press ing lug 53 inside the said case 52 until passing bridge 56, the lug 53 being locked ~hen returning to its initial position out-' .
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2 0 ;~ 3 ?, 19.-side case 52. Said locking system preverlts the pressure of lug53, which can only be unlocked by the corresponding key, in case the user is a chil-l.
Band so can be Eixed at any part o~ thc user's body, such as by the ankle "~aist, arm or ncc~, and has the transmitter means 20 attached thereto with electrodes 30 of activating means 23 exposed, so that, l~hen in contact with water, the circuit is closed and the remote signal transmitter means 20 is activated.
Activating means 23 of the remote signal transmitter means 20 can have variations regarding the above described pattern, since electrodes 30 can be covered by a water-proofing adhesive tape, so that the activating means 23 can be immersed in water and is only activated wllell tllC use~ rcmoves said adhesive tape and closes the circuit by electrodcs 30coming into contact with water.
Another alternative use of this invention byswimmers consists in placing the activating means 23 in a watertight case, i ~"
with a swltcher operated by pressure through a flexible wall of said watertight case.
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Claims

1. An alarm system for detecting persons who accidentally fall into the water and who ale eventually in the water in an emergency situation that requires help, of the kind comprising a signal transmitter means including an activating means for actuating said transmitter means which is sensitive to a pre-determined condition, said transmitter means being attached to the body of the user by removable means of attach-ment, and, at least, a receiver means for receiving said signal and capable of identifying the signal and controlling an alarm device disposed at a place where help is needed.

2.- A system according to claim 1, characterized in that the transmitter means is a device transmitting high-frequency radio signals.

3.- A system according to claim 1, characterized in that the signal of the transmitter means is a codified signal and the receiver means receiving said signal is capable of detecting said codified signal and controlling an individual alarm for said codified signal.

4.- A system according to claims 1 and 2, characteriz ed in that each of said transmitter means transmits individual codified signals and said receiver means receiving said codified signals operates a different alarm for each codified signal.

5.- A system according to claims 1 to 4, characteriz ed in that it comprises a signal transmitter means including an activating means for activating said transmitter means sensitive to a pre-determined condition, said transmitter means being attached to the body of the user by removable means of attach-ment, at least a means for collecting and repeating said signal, disposed in a fixed site on the water medium, and at least a receiver means for receiving said signal and capable of identify ing said signal and operating an alarm device.

6.- A system according to claims 1 to 4, characteriz ed in that it comprises a signal transmitter means including an activating means for activating said transmitter means sensitive to a pre-determined condition, said transmitter means being attached to the body of the user by removable means of attachment this system further comprising at least two receiver means for receiving said signal and capable of identifying said signal and operating an alarm device, said receiver means being arranged on the coast ground and spaced one from the other so as to cover a particular area of the adjacent water medium, said alarm device being connected to a means for locating the place from where the signal of the transmitter means is emitted as determined by the joint operation of said receiver means

7.- A system according to claims 5 and 6, characteriz ed in that it comprises a signal transmitter means which includes an activating means for activating said transmitter means sensitive to a pre-determined condition, said transmitter means being attached to the body of the user by removable means of attachment, at least a means for collecting and repeating said signal, arranged in the water medium, at least two receiver means for receiving said signal and capable of identifying said signal and operating an alarm device, said receiver means being arranged at the coast and spaced one from the other so as to cover a particular area in the adjacent water medium, and said alarm device being connected to a means for locating the place from where the signal of the transmitter means is emitted as determined by the joint operation of said receiver means.

8.- A system according to claims 5 to 7, characteriz ed in that the means for collecting and repeating the signal includes an amplifier of said signal.

9.- A system according to claim 1, characterized in that the alarm signal is of a progressive intensity.

10.- A system according to claim 1, characterized in that the alarm signal includes a control circuit that detects a temporary signal as different from a continuous signal.

11.- A system according to claims 5 and 7, characteriz ed in that each means for collecting and repeating said signal is arranged on an anchored buoy.

12.- A system according to claims 5 and 7, characteriz ed in that said means for collecting and repeating the signal is arranged on a pile.

13.- A system according to claims 5 and 7, charactcriz ed in that each means for collecting and repeating the signal is arranged on a wall.

14.- A system according to claims 6 and 7, characteriz ed in that the locating means is a radiogonometry device.

15.- A system according to claims 1, 5, 6 and 7, characterized in that the activating means is formed by a pair of exposed electrodes which are interposed in the current feeding circuit of the transmitter means.

16.- A system according to claim 15, characterized in that the pair of electrodes is covered by a water-proof tape which can be manually removable.

17.- A system according to claims 1, 5, 6 and 7, characterized in that the activating means is formed by a switch arranged on the current feeding circuit of the transmitter means, which is within a watertight housing and is operated from the outside.

18.- A system according to claims 1, 5, 6 and 7, characterized in that the transmitter means is a device for transmitting UHF or VHF high-frequency radio signals.

19.- A system according to claim 1, characterized in that the transmitter means is a device for transmitting audio-frequency signals.

20.- A system according to claim 1, characterized in that the transmitter means is a device for transmitting ultra-sound signals.

24.-

21.- A system according to claim 1, characterized in that said signal receiver means includes an antenna perimetrically disposed with respect to the water medium.

22.- A system according to claims 1, 5, 6 and 7, characterized in that the means for removable attachment to the body of the user includes a safety lock system which prevents the user from unlocking it by himself.