Abstract:
An anti-theft alarm tag comprises two parts ( 10,12 ) which shall be located on opposite sides of a product ( 11 ) with a pin ( 14 ) on one part ( 12 ) extending through the product and locked together with the other part ( 10 ). Said one part forms a housing comprising a bottom ( 15 ) and a cover ( 16 ) and enclosing an alarm device ( 20 ) and a circuit board ( 18 ) with an electronic circuit controlling the alarm device. The pin is connected to the cover or the circuit board and extends through the bottom with slide fit, contact means ( 39 ) being switched for activating the alarm device by deformation of the cover or the circuit board, respectively, following an attempt to separate the two parts of the alarm tag.

Description:
FIELD OF THE INVENTION 
   The present invention relates to an anti-theft alarm tag comprising two parts, one of which is provided with a pin attached to said one part to be located on one side of a product with the pin extending through the product into locking engagement with the other part, which is to be located on the opposite side of the product. Said one part has a housing which includes a bottom and a cover and encloses an alarm device and an electronic circuit controlling the alarm device. The pin is connected with a deformable element, and contact means in said electronic circuit are switchable to trigger the alarm device by deformation of said element following an attempt to separate said parts. 
   BACKGROUND 
   An alarm tag of this type is disclosed in WO 95/27959. In the prior art alarm tag described in this publication the pin is attached to a bottom wall of the housing. Also a bi-stable spring washer is attached to said bottom wall. This washer is operatively related to the electronic circuit and forms a contact element which is normally in a first position in which the alarm device is silent, but is switched via the pin to a second position at attempt to separate the two parts of the alarm tag. 
   An important aspect relating to anti-theft alarm tags of the type referred to is the manufacturing cost of the tag since the tag is a product which is sensitive to price. 
   Another aspect is that among shop-keepers there is a great demand for alarm tags that are not only cheaper but also smaller and thinner than those available on the market today. 
   SUMMARY OF THE INVENTION 
   A primary object of the present invention is to provide a most reliable anti-theft alarm tag of the type referred to, which can be made small and thin and can be manufactured at low costs. 
   This object as well as further objects that will be apparent to the skilled man by the description which follows are achieved according to the invention by an alarm tag of the kind referred to above, which is characterized by the features of claim  1 . Further features of the invention are defined in the dependent claims. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
     Illustrative embodiments of the alarm tag of the invention will be described below with reference to the accompanying drawings, in which 
       FIG. 1  is a side view of an alarm tag attached to a product shown fragmentarily in cross section; 
       FIG. 2  is an enlarged cross sectional view of that part of the alarm tag which comprises a pin and a housing, in a first embodiment of the invention; 
       FIG. 3  is a cross sectional view taken along line III-III in  FIG. 2 ; 
       FIG. 4  is a plan view of a bottom of the housing in  FIGS. 2 and 3 , as seen from the inside thereof; 
       FIG. 5  is a plan view of a cover of the housing as seen from the inside thereof with a circuit board mounted therein, 
       FIG. 6  is a fragmentary enlarged cross sectional view of the housing disclosing a contact device forming part of the electronic circuit, 
       FIG. 7  is a plan view of a battery lid as seen from the inside thereof, 
       FIG. 8  is a side view of the battery lid, and  FIG. 9  is a cross sectional view similar to that in  FIG. 2  of a second embodiment of the invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   In  FIG. 1  there is shown an alarm tag which comprises a first part  10  including a lock mechanism. Part  10  is applied to one side of a product  11 . The alarm tag also comprises a second part  12  including a housing  13  with a pin  14  and enclosing an alarm device. Part  12  is applied to the opposite side of product  11  with pin  14  extending through the product. The pin is easily pushed axially into part  10  but is firmly gripped by the lock mechanism if it is attempted to displace the pin in the opposite direction. Part  12  is thus attached to part  10  by the lock mechanism in such a way that the parts cannot be separated for removal of the alarm tag from the product unless the lock mechanism is operated magnetically or mechanically in a release device at the site in a department store or shop where the product is to be paid for. The lock mechanism can be of any type known in the art including latch members which engage the pin but can be disengaged by mechanical or magnetic actuation by means of the release device, reference is made e.g. to U.S. Pat. No. 5,275,122. 
   The alarm device is activated if the alarm tag is carried out from a defined area in a department store or a shop due to the fact that the alarm tag then, at the exit from said area, will leave an electromagnetic or electrostatic field maintained in said area, or is carried through such a field maintained between bows located one, at each side of an exit passage, in accordance with a well known technique applied in connection with alarm tags. 
   With reference primarily to  FIG. 2 , housing  13  comprises a bottom  15  and a cover  16  which are made of an impact resistant and preferably elastically deformable material, e.g. polycarbonate, and are welded or fused together at  17 . In the space defined by the bottom and the cover there is mounted a circuit board  18  which on the upper side thereof engages protrusions  19  in the cover, which keep the circuit board in a fixed position in the space defined by the bottom and the cover. 
   A circular sound washer  20  rests on a sharp edge of a circular rim  21  projecting from the upper side of bottom  15 , and is attached to the rim by means of an elastic glue, double-stick tape, or any other suitable adhesive. The sound washer includes a circular piezoelectric layer  22  on the upper surface thereof. This layer can be made as a circular disc which is attached to the upper surface of the washer, e.g. by means of an adhesive. 
   Openings  23  are provided in the bottom for the insertion of two batteries  24  and  25 , of which one has a positive pole facing upwards and the other a positive pole facing downwards. The bottom has upstanding guide formations  26  for localizing the batteries in the correct position, see  FIG. 4 . A lid  27  for covering openings  23  has spring hooks  28  which at closing of the lid engage sloping surfaces formed by the bottom, the hooks being deflected by sliding against said surfaces when the lid is pushed against the lower side of the bottom to close the openings. The hooks snap into engagement with shoulders  29  in the closed position of the lid. 
   As shown in  FIG. 5 , circuit board  18  has contacts  30  for connection of the batteries to the circuit on the circuit board. A spring blade  31  is provided as a contact element connecting the batteries in series, see  FIG. 3 . There are also on the lower side of the circuit board contact blades  32  which connect the sound washer with the circuit board, see  FIG. 5 . 
   According to a first embodiment, shown in  FIG. 2 , pin  14  has a head  33  and is received in a bore  34  in cover  16 , which preferably is shaped such that the head is flush with the upper surface of the cover. A knurled portion  35  of the pin having limited axial length is received in bore  34  with pressure fit so that the pin is attached to cover  16 . The pin extends through a bore  36  in bottom  15  with sliding or clearance fit in said bore, and projects from the lower side of the bottom. A semi-circular rib  37  is formed by the bottom at the lower side thereof with the center in bore  36  and this rib makes it difficult to apply pincers against the pin at an attempt to cut the pin between the two parts of the alarm tag. The rib preferably does not extend all the way around the pin as there must be clearance for the battery lid to be mounted and demounted. 
   With reference to  FIG. 5 , the circuit board forms a tongue  38  with a contact blade  39 , which contact blade is attached to the circuit board at one end and is inclined towards the bottom at its other end. Normally this contact blade is supported at the other end by a projection  40  on the battery guide formation  26 , see  FIG. 6 . In this position the contact blade is spaced from an associated contact  39 A on the lower side of the circuit board but can be engaged with this contact by flexing of the cover towards the bottom of the housing such that circuit board  18  and particularly contact  39 A is brought into contact with contact blade  39  at projection  40 . When the alarm tag is applied to a product with the two parts of the tag located on opposite sides of the product and with the pin penetrating the product and locked in part  12 , any attempt to separate the two parts  10  and  12  of the alarm tag will consequently cause yielding of the cover towards the bottom so that contact blade  39  will be pressed upwards against the associated contact on the circuit board, which triggers the alarm circuit, including an oscillator circuit and a holding circuit both provided on the circuit board. When the alarm is triggered the oscillator circuit is energized so that the sound washer produces sound and is kept producing sound by means of the holding circuit until this circuit is reset. Reset is effected by short-circuiting battery  24  by means of a needle (not shown) that is applied against contact element  31  through an aperture  41 , see  FIG. 3 , which is not available until the two parts  10  and  12  have been separated. Accordingly, the alarm cannot be stopped until the two parts of the alarm tag have been separated by authorized staff. By means of the needle acting against the contact element  31 , battery  24  is short circuited between the positive pole thereof and the shell of the battery. The holding circuit and thus the alarm circuit cannot function with one battery only energizing the holding circuit. Openings  42  are provided in the housing so as to allow the sound produced by the triggered alarm tag to propagate into the surroundings of the tag, see  FIG. 2 . 
   The housing of the alarm tag of the invention can be stored without the pin and then when it is to be used can be provided with a pin of suitable length and thickness for combination with a desired part  12 . 
   In the embodiment described, lid  27  can be replaced by an integral part of the bottom which means, however, that the batteries are located in the housing before cover and bottom thereof are interconnected at  17 , and then cannot be exchanged. A second embodiment disclosed in  FIG. 9  has a battery arrangement of this type, although it should be realized that this battery configuration is equally applicable to the design of the attachment of the pin to cover  16  in  FIG. 2 . In the embodiment of  FIG. 9 , rib  37  extends over a complete circle because no space is required for mounting and demounting a battery lid. 
   The second embodiment includes a further modification, in that pin  14  is attached to circuit board  18  rather than to cover  16 . The circuit board is resiliently flexible, and contact blade  39  is mounted in order to function as described in connection with the first embodiment so that when the pin is manipulated in an effort to remove the alarm tag from the product protected by the tag the circuit board will flex and the contact blade will close the electric circuit to trigger the alarm. Otherwise the second embodiment is identical with the first embodiment. 
   It has been found that alarm tags of similar type as that described herein can be brought out of order by heating the pin by means of a lighter. A specific embodiment of the present invention is devised to overcome this problem. According to this solution, contact blade  39  is inherently biased to take a position in which it is set against the associated contact  39 A on the circuit board, but is withheld from this position by a connection element or spacer of wax or another fusible material (not shown) which keeps contact blade  39  spaced from the associated contact  39 A on the circuit board. If the connection element or spacer melts due to warming of the pin contact blade  39  due to the inherent bias will bend against the associated contact on the circuit board and thus will trigger the alarm.