Abstract: A miniature magnetic article surveillance system marker is adapted, when armed, to resonate at a frequency provided by an incident magnetic field applied within an interrogation zone. The marker comprises a magnetomechanical element having at least one elongated ductile strip of magnetostrictive ferromagnetic material disposed adjacent to a ferromagnetic element which, upon being magnetized, magnetically biases the strip and arms it to resonate at said frequency. A substantial change in effective magnetic permeability of the marker at the resonant frequency provides the marker with signal identity.

Abstract: An apparatus for prescreening an individual about to be subjected to a security screening including a magnetometer. The prescreening device comprises a base housing having a top panel, and a plurality of downwardly extending sidewalls. The base housing is adapted to adjustably support a metal detector within the base housing such that when an individual places an object, such as a shoe, in proximity to the base housing, the metal. detector detects the presence of metal, weapons, explosives, or other contraband in the object, thereby alerting the individual that the object may contain enough material to alarm the magnetometer. The individual may then take the necessary steps to remove the object from their persons, thereby possibly reducing the number of potentially false magnetometer alarms.

Abstract: Each of a plurality of satellite nodes coupled to a sensing device or an actuator and logically dispersed around an access node are configured to wirelessly communicate alarm conditions. A first satellite node detects and accesses an alarm condition and then prepares an alarm message containing an alarm code corresponding to the alarm condition and an address indication. The first satellite node may thereafter receive alarm messages from other satellite nodes logically further from the access node than the first satellite node. Alarm codes contained in the received alarm messages are filtered and compared to the alarm code of the prepared alarm message. The first satellite node includes a sender address in the prepared alarm message for each received alarm message containing an alarm code that matches the alarm code of the prepared alarm message. The first satellite node transmits the prepared alarm message to the access node.

Abstract: A device for detecting the presence of objects in a vehicle's blind spot. The invention relates to a device for detecting the presence of objects in a vehicle's blind spot, where the objects contain at least one ferromagnetic material whereby they distort the earth's magnetic field. The device is mounted on a vehicle that has at least one blind spot. The detection device can detect the object located in the blind spot because it is provided with a unit for detecting the distortion of the earth's magnetic field caused by the object. Preferably it includes a logical circuit with neural nets for processing the signals received from the sensors.

Abstract: A system is provided for determining the type of vehicle which has never been sensed before that is transiting between a cluster of acoustic and seismic sensors by graphing an acoustic source level against a seismic source level for the vehicle, with light vehicles such as pick-up trucks being distinguished from heavy tracked vehicles such as tanks by where on the graph the plotted point for a vehicle lies.

Abstract: A door system includes an antenna-based proximity sensor with a releasable electrical connector that enables the sensor to function with a breakaway feature of the door. The sensor includes a signal generator and a door-mounted antenna for sensing a body or an obstruction near the door. The signal generator (or oscillator) can be installed at various locations between a power source and the antenna. In some cases, the wiring between the antenna and the power source includes a rotatable feature to accommodate the rotation of a drum that carries a wrap-up, pliable door panel. The rotatable feature may be a rotatable electrical connector, or it may be a wire having sufficient length and flexibility to twist about itself within the hollow interior of the drum.

Abstract: A detachable entrance and exit gate with a combined commodity burglarproofing and small arms detecting system including a detachable entrance and exit gate with a pair of vertical type panels which are oppositely disposed inside of an entrance and exit door, a central processing unit connected with the transmitting and receiving signal frequency coil portions, an image-receiving device, a warning flare and a photographing device which are controlled by a central processing unit, where the small arms detecting transmitting coil portion and the commodity burglarproofing transmitting coil portion are interiorly installed at one side of the vertical type panel of the entrance and exit gate and the small arms detecting receiving coil portion and the commodity burglarproofing receiving coil portion RX2 are interiorly installed at one side of the other vertical type panel of the entrance and exit gate, so that a variation existing between a frequency zone of the small arms detecting transmitting and receiving coil p

Abstract: A steerable electromagnetic induction (EMI) sensor system for measuring the magnetic polarizability tensor of a metal target. Instead of creating a vertical magnetic field from a horizontal loop transmitter configuration used by most prior art EMI metal detectors, the transmitter geometry of the sensor system's antenna is designed especially for creating multiple horizontal and vertical magnetic fields and for steering the same in all directions. The horizontal magnetic field (HMF) antenna has the potential advantage of a relatively uniform magnetic field over a large volume. A second potential advantage of the HMF antenna is that compared to a conventional loop antenna, the magnetic field intensity falls off slowly with distance from the plane of the antenna. Combining two HMF sensor systems creates a steerable two-dimensional magnetic field sensor. Combining the steerable HMF sensor with a vertical magnetic field antenna forms a three-dimensional steerable magnetic field sensor system.

Abstract: The security portal (10) is dimensioned to be readily mounted and transported on a trailer (54) alone as a single security portal (10) or with a plurality of security portals to provide screening for a short term, high security event. The portal (10) includes bullet-resistant, bomb-blast proof and at least partially transparent walls (12, 14, 16, 18) and doors (22, 24, 26). Monitors (32, 34) are secured to the portal (10) for monitoring an individual within an interior (30) of the portal (10) for detecting weapons, bio-hazards, chemical toxins, illegal drugs, contraband, or other hazardous materials. The security portal also includes a security monitoring station (36) adjacent the security access door (26) and a bomb-blast enclosure (66) having a flap (68) and bomb-blast containment balloon (70) for containing hazardous materials in the event of a bomb-blast within the portal (10).

Abstract: An installation includes at least one magnetic field source, measuring equipment fixed onto a freely movable object whose motion is to be detected, and control equipment. The measuring equipment includes a magnetometer able to measure the magnetic field it is surrounded by, a comparator able to test the magnetic field value against a threshold value, and a transmitter for transmitting a signal representing the result of this test. The control equipment receives this signal and derives therefrom the object displacement and/or its proximity to the source.

Abstract: The present invention is a technique for locating and identifying a failed filter/arrester in an underground conveyance such as a fiber optic cable. A sensor is installed in the filter/arrester housing to sense grounding of a cable locating frequency. The sensor will monitor the cable locating signal that is normally on the cable and blocked by the filter arrester to ground. A small radio frequency oscillator (85 to 88 Hz), also installed inside the filter housing, is activated by the sensor. The RF signal is detected above ground with standard cable locating equipment. A warning indicator such as an indicator light may also be installed on the outside of the filter housing. The indicator is also activated by the sensor. In that way, the particular failed filter can be identified if multiple filters are installed at that location. The power that will be required to operate the RF transmitter and indicator will be obtained from the voltage passing through the cable.

Abstract: A radio frequency (RF) data carrier is presented. The RF data carrier comprises at least one diffraction element that has a dimension of the order of a wavelength of RF radiation and is responsive to RF irradiation, the response produced by the diffraction elements in the data carrier being indicative of machine-readable data carried by data carrier.

Abstract: A Wide Area Metal Detection (WAMD) system and method for security screening a crowd of people is provided. The system comprises at least one Magnetic Field Generator (MFG), e.g., a Horizontal Magnetic Field Generator (HMFG) buried below a walking surface for generating a magnetic field, a plurality of magnetic field sensors located within the sensing area of the MFG for sensing a metallic object, based on eddy currents in the magnetic field, and a location indicator for indicating a location of an individual with the metallic object at a position corresponding to that of one of the plurality of magnetic field sensors that sensed the metallic object. At least one video camera is included for identifying the individual at the location indicated by the location indicator and tracking further movements of the individual.

Abstract: Door sensor(s) may be attached to a door body or bodies of automatic swing doors. The door sensor(s) may be equipped with door position detectors including geomagnetic sensor(s), the sensor(s) being itself or themselves capable of detecting position(s) occupied by the door body or bodies during opening and/or closing thereof. During opening and/or closing of the door body or bodies, determination may be made as to whether detected object(s) are object(s) intended for detection; and in the event that object(s) are object(s) intended for detection, opening and/or closing of the door body or bodies may be stopped, slowed, and/or reversed in correspondence to detected position(s) occupied by the door body or bodies during opening and/or closing thereof.

Abstract: A metal detecting device for the detection of a metal object concealed in shoe or on a leg of a subject, including: a housing with a platform having an upper surface with indication areas thereon for the correct positioning of each of a subject's feet, left-foot and right-foot electromagnetic coils under the indication areas connected to a power supply via an oscillator and a switch, an electromagnetic shield divider between the left-foot and right-foot electromagnetic coils, a detection system for the detection of the placement of the subjects feet on the indication area, a processing unit for processing signals from the electromagnetic coils and detection system, and a display connected to the processing unit for displaying a warning signal if metal is detected.

Abstract: A multi-mode electromagnetic target discrimination sensor system for transmitting an electromagnetic signal and receiving a reflected signal from at least one target is disclosed having a variable inductance antenna having a variable inductance transmitter and a variable inductance receiver for varying at least one of operating bandwidth, sensitivity and size of the antenna, a processor for alternating between a time domain operating mode and a frequency domain operating mode, and controlling the variation of the inductance of the variable inductance antenna based on a current operating mode, and at least one processing algorithm for receiving signals from the receiver, discriminating targets from the received signals, and outputting the discrimination results is disclosed.

Abstract: A method and device for activation of large quantities of security elements for the electronic article protection. The security elements are exposed to at least one magnetic field produced by one or more coils carrying a line current subjected to sine oscillations. The coils are supplied with current pulses that are shorter than the sine oscillations. The amplitude of the current pulses diminishes as a function of time.

Abstract: A tamper resistant magnetic contact switch apparatus for alarm systems that has a plurality of magnetic reed switches configured in a logic circuit and a magnetic pack for actuation. A magnetic shield disposed around the switches defines an actuation zone. In combination with the magnetic shield preventing magnetic fields from reaching the switches from locations outside the actuation zone, the magnet pack activates two of the five switches when positioned within the actuation zone to complete the logic circuit. The magnet pack does not, however, activate any of the other switches. If any of the other three switches are activated, or if either of the two activated switches are deactivated, the logic circuit is broken and the alarm circuit is activated.

Abstract: An antenna arrangement comprises at least two antenna loops disposed and overlapping in a plane to define a detection region adjacent thereto in which the antenna loops transmit and/or receive electromagnetic signals and through which a wireless article may pass. The antenna arrangement may be coupled to a processor and/or utilization system for performing a desired function.

Abstract: A displacement sensing system including an oscillator circuit having a characteristic frequency which varies as a function of a magnetic field in the vicinity thereof, an element whose position relative to the oscillator circuit is varied by a displacement, the element being operative to vary the magnetic field in the vicinity of the oscillator circuit as a function of the displacement and circuitry for sensing a change of frequency of the oscillator circuit over time (delta f/delta t) and for providing an output indication when the change in frequency of the oscillator circuit over time exceeds a threshold.

Abstract: A device representing a simple means of multiplying the functionality of wiring in point to point control circuits such that fault tolerant, fault reporting circuits can be constructed with less wire. The circuit can employ the wiring on a continuous basis by the use of AC and a series arrangement that may combine sensors and command loads on the same single wire loop. A bi-directional current detector with switchable impedance over each polarity can form the device. The detector may be equipped with an electrically isolated man-machine interface that communicates with light to achieve input-output functions. Command functions may be issued by changing the current level within the circuit over each polarity of current flow to series mounted remote loads that are polarized with diodes. The whole circuit can be in triplicate for high reliability and fault tolerance and use a common return wire.

Abstract: A portable alarm system includes a cigarette lighter socket mount which is useful to deploy a flexible beam structure in cantilever. An electrical board mounted eccentrically from the other end of the beam structure then provides the torsional and bending motions that are inducted in the course of illegal entry, these motions then being sensed by tank circuits connected to corresponding comparators. The output of each comparator is then combined in a logical AND and OR combination that is manually selected by a switch to turn on a sending unit that then communicates with a remote device like a pager.

Abstract: The present invention is a magnetic field detection device that makes use of a frequency characteristic affording circuit in order to selectively detect magnetic signals from a frequency domain accurately at a high level of sensitivity. The present invention has a magneto-impedance element, a detector coil and a negative feedback coil which is wound around the magneto-impedance element, and a frequency characteristic affording circuit which affords a frequency characteristics on the negative feedback signal of a negative feedback connecting an output terminal thereof with the negative feedback coil. Using filters as the frequency characteristic affording circuit, the following are possible uses of this magnetic field detection device: a geomagnet detection device for earthquake prediction (using a high-pass filter), a bill validation apparatus for vending machines, etc. (using a low-pass filter), and a magnetic oscillation detection device for a magnetic gate system (using a band-reject filter).

Abstract: The invention concerns a system for detecting multiple tags in a detection zone. The system includes an electronic tag detection system having first and second field generators, each having a respective antenna for generating an electromagnetic field in a detection zone defined between the antennas. Additionally, at least one of the field generators can be responsive to a presence of at least two electronically detectable tags in the detection zone, for varying an intensity of at least one of the electromagnetic fields.

Abstract: A weapon detector system including a detecting gate which is placed on the inside of an entrance; a central processing unit connected by wire with transmitter coils and receiver coils of the detecting gate; and an image receiving device, a warning indication lamp and a photographing device that are wirelessly controlled by the central processing unit; wherein the detecting gate includes side panels connected together, a first side panel containing the transmitter coils and a second side panel containing the receiver coils, the first and second side panels standing on opposite sides of the entrance facing each other, and the insulating material situated on a suitable position of a metallic frame surrounding the entrance for preventing a scattering and vortex phenomenon.

Abstract: A target junction is illuminated with energy at a fundamental RF frequency and reflections from the non-linear junction are analyzed to determine the type of junction detected. The power output level of a transmitter emitting the illuminating signal is automatically controlled so as to drive the signal strength of the received signals towards a predetermined value, e.g. a minimum threshold value. An indication of the current received signal strength, adjusted by a factor so as to compensate for any automatic adaptation in the actual transmitter power output level, may be provided to an operator.

Abstract: The present technology involves a method and apparatus for detecting and reporting magnetic fields in the proximity of a utility meter as an approach to determining tampering of such meter. The sensitivity level of the magnetic field sensors may be adjustable allowing either remote or local sensitivity adjustments to a magnetic field sensor to compensate for variations in the electromagnetic environments of different meter installation sites. Alternatively, the output of each magnetic field sensor may be connected to the input of an adjustable threshold circuit. When the output voltage of the magnetic field exceeds a predetermined threshold voltage, a magnetic event signal is generated. Threshold adjustments to the adjustable threshold circuit may be performed locally at the meter site or remotely from a station. The output of each magnetic field sensor may be monitored by a locally or remotely programmable magnetic sensor output monitor.

Abstract: A driveway security sensor having a ground-engaging member connected to a housing body. The ground-engaging member substantively has the shape of a slake. A swivel member is pivotally connected to the housing body, and a motion sensor is connected to the swivel member.

Abstract: A high-voltage-proximity warning system has a local panel (1) for being positioned in or about a cab (2) of heavy equipment or other vehicle (5), a remote panel (3) in predetermined electrical communication with the local panel and one or more proximity antennas (4) for being positioned selectively on the vehicle in predetermined electrical communication with the local panel. The local panel is adapted to be push-button operable conveniently by an operator with gloved hands in a position where it is readily visible and easily connectable electrically to the remote panel and to the one or more proximity antennas. The remote panel is adapted to be positioned on or off of the vehicle where it can be protected for supportive operation and accessed for plural electrical connection to electrical devices that can include an electrical-source terminal (11), to speakers, and to warning and alarm communication devices (50).

Abstract: A trashcan mounted apparatus for scanning for metal objects is provided. The apparatus includes a mounting lip adapted to conform to the top periphery of the trashcan and adapted to removably mount to and surround the aperture of the trashcan. A funnel shaped entryway extends from the mounting lip. A plurality of vertical walls are below the mounting lip and the top periphery of the trashcan and are attached to the funnel shaped entryway and form an opening to the trashcan. A detector coil surrounds the vertical walls for detecting metal passing through the opening. Control electronics coupled to the detector coil includes a speaker and a light indicator for warning that the detector coil has detected metal passing through the opening. A counter displays the number of times the detector coil has detected metal passing through the opening. A gain adjust is provided for adjusting the sensitivity of the detector coil.

Abstract: A device for detecting the presence of objects in a vehicle's blind spot. The invention relates to a device for detecting the presence of objects in a vehicle's blind spot, where the objects contain at least one ferromagnetic material whereby they distort the earth's magnetic field. The device is mounted on a vehicle that has at least one blind spot. The detection device can detect the object located in the blind spot because it is provided with means for detecting the distortion of the earth's magnetic field caused by the object. Preferably it includes a logical circuit with neural nets for processing the signals received from the sensors.

Abstract: A system and method for scanning individuals for illicit objects include the ability to scan a wheeled user transport device and an individual being transported thereby for metallic objects and to determine whether an illicit object may be present, without activating an alarm for the user transport device while detecting illicit objects on the individual.

Abstract: An apparatus is provided for use with capacitive presence detection systems. The apparatus includes a sensor (10) in the form of a tape which may be adhesively affixed to an object such as a parking gate (4) arm. Additionally, spaces for use in mounting the sensors (40) are disclosed which increase the depth of field of the sensor. The tape is a sandwich having a plastic film top layer, a metallic foil middle layer, and a plastic bottom layer having an adhesive material.

Abstract: A portable walk through metal detector with interchangeable sensor panels and other structural members that can be quickly assembled, or disassembled and transported. The device includes two structural base members to anchor the archway, multiple sensor panels with which the sides of the archway are constructed, and a top cross-member to join and support the walls of the archway. In addition, the top cross-member provides a vehicle platform for moving a disassembled unit with built-in wheels, a handle, and stacking structures to support the other members.

Abstract: A metal detection circuit that includes a power source and a connection to ground. At least one transmitter circuit is electrically coupled to the power source and ground and a transmit coil is electrically coiled to the transmitter circuit. At least one receiver coil has provided along with an amplifier to be electrically coupled to the receiver coil. An integrator is electrically coupled to the amplifier and a track/hold circuit is electrically to the integrator. A filter is electrically coupled to the track/hold circuit and an output. The circuit provides a high amplitude, low duty cycle excitation pulse, which allows for the sensitivity of a high level excitation signal with the power economy of a much lower energy excitation signal. The receiver circuit collects and conditions the signals resulting from the relatively short duration, large amplitude excitation pulse, and goes in to hold mode during the relatively long charge and idle periods.

Abstract: A system and method for centralized security screening of packages including baggage. The system creates images and data concerning baggage to be reviewed, packetizes the data long with additional identification information, and conveys the data packets to a central screening location. All analysis of the baggage information is accomplished in a centralized way with risk assessments being provided to each image. Upon sensing of a package or baggage of concern, alerts may be sent to the screening location for action. Artificial intelligence tools are used to pre-screen images to assist with workload assignment.

Abstract: A magnetic induction device mounted at the wellhead that is capable of measuring changes in magnetic flux can recognize when a tubing joint or casing collar passes in or out of the well. The number of changes in magnetic flux directly correlates to the number of joints and collars that have passed, and therefore an accurate inventory of the number of lengths of casing or tubing that are run into the well can be automatically maintained.

Abstract: A metal detector that includes a substantially non-metallic housing that defines a hollow cavity and a human walking surface and a metal scanner element positioned in the hollow cavity defined by the non-metallic housing, wherein the walking surface receives a covered human foot. This invention allows travelers to leave their shoes on while transiting security checkpoints.

Abstract: A metal detector (1) used for identifying contaminants in products. The detector (1) includes an oscillator coil (10) that may be formed as two series wound coils (34, 35) having relatively smaller dimensions or as two parallel wound coils (29, 30) having relatively larger dimensions. A pair of input coils (13, 14) is located adjacent to the oscillator coil (10). A first signal (8) is generated by the first input coil (13) in response to the presence of a metallic object, while a second signal (24) is generated by the second input coil (14) in response to the presence of a metallic object. By measuring the ratio of the first signal (8) to the second signal (24) the physical location of a metal object within the metal detector cavity (7) can be determined.

Abstract: A method of determining differing characteristics of magnetic dipole elements such as orientation, coercivity, bias and response amplitude and a tag reader for reading magnetic tags containing such elements. The elements are scanned by a rotating magnetic field and two sets of transition data are determined. The transition data sets are associated with respective elements and analyzed to determine mean field values resolved along the element vectors. These field values are used to determine properties of the elements, such as coercivity.

Abstract: A testing device is operative to sense or monitor a radiated field emitted by a solid state transformer/igniter and to indicate the detection corresponding to an operating state of the transformer/igniter.

Abstract: In general, the invention is directed to techniques for creating and controlling a magnetic field for use with electronic article surveillance (EAS) markers. In particular, the techniques make use of current switching devices to generate a signal having one or more current pulses for creating the magnetic field. An electronic article surveillance (EAS) system includes a coil to create a magnetic field for changing a status of an EAS marker and a drive unit to output a signal having one or more current pulses for energizing the coil. A programmable processor within the EAS system controls the drive unit to generate the output signal according to a desired profile. By selectively activating and deactivating current switching devices within the drive unit, the processor can direct the drive unit to generate the output signal according to a desired profile having a number of current pulses of different amplitudes and direction.

Abstract: This invention concerns a metal detector comprising transmitting coils, receiving coils and an electronic processing circuit adapted to detect variations in the signals received by the receiving coils against a reference value, characterised in that it also includes a test module which has selection means able to detect a test request, and control means, used when a test request is detected by the selection means, able to compare the signals from the receiving coils during the subsequent passing of a known standard reference object with a predetermined response through the detector. This invention also concerns a test procedure.

Abstract: An apparatus for detecting ferromagnetic objects in the vicinity of a magnetic resonance imaging scanner. The apparatus comprises primary sensor means adapted to measure a magnetic field, arranged in communication with signal processing means configured to identify temporal variations in the measured magnetic field due to the movement of a ferromagnetic object within an ambient magnetic field and to provide an output indicative of the presence of a ferromagnetic object in the vicinity of the primary sensor means. The apparatus further comprises secondary, non-magnetic, sensor means adapted to detect the movement of objects in the vicinity of the primary sensor means in order to reduce false alarms. The output from the signal processing means may be used to operate an audible alarm, a visual alarm, an automatic door lock or a physical barrier.

Abstract: An impact-induced pulse sensor comprises a housing having a longitudinal axis and a guiding element arranged on the housing. A sensor element is adapted to be displaced within the housing along the guiding element when an essentially pulse-shaped impact of a given duration is exerted on the housing. The sensor element is displaced with a predetermined speed and along a predetermined distance. The guiding element is configured such as to affect the speed. The sensor element is made of a magnetic material. A pickup element is rigidly connected to the housing for magnetically generating a measuring signal derived from the displacing of the sensor element caused by the impact. The sensor element, when displaced, generates in the pickup element a measuring voltage depending from the distance. The guiding element affects the speed such that for impacts with like pulse areas the measuring voltage vs distance is independent from the duration of the pulse-shaped impact.

Abstract: A metal detecting device for the detection of a metal object concealed in shoe or on a leg of a subject, including:

Abstract: A device (12) facilitates sealing and tracking of a container (18). The device includes a bolt (166) which extends through openings in a latch mechanism (19) on the container. The bolt also passes through spaced coils (251, 252) of the seal device. The seal device uses one coil to generate a magnetic field, while monitoring the corresponding magnetic field induced in the other coil. Tampering with the bolt affects the magnetic field, which in turn permits the seal device to detect the tampering. The seal device periodically transmits wireless signals (71), which can be remotely received for purposes of tracking the container and monitoring the integrity of the seal.

Abstract: A magnetic marker for use in an article surveillance system, and an electronic article surveillance system utilizing the same are presented. The marker comprises a magnetic element including a predetermined number of microwire pieces made of an amorphous metal-containing material coated with glass and having substantially zero magnetostriction, coercivity substantially less than 10 A/m, and permeability substantially higher than 20000, the predetermined number of the microwire pieces and a core diameter of the microwire piece being selected in accordance with a desired detection probability of the marker to be obtained in a specific detection system.

Abstract: Disclosed is a method and an apparatus implying nearly 100% security with a tag system showing low cost and compact volume. Like a conventional tag, the disclosed tag system will respond properly to an interrogation signal. In addition, the disclosed tag system is able to monitor the environment local to a merchandise. Whenever the merchandise package is opened and/or impaired, alarm will be generated on the spot. It is almost impossible to disarm the tag system, unless a password is attained. The disclosed tag system shows a high sensitivity, and it does not need an electronic searching machine, or an interrogation gate, to operate. When combined with an electromagnetic transmitter, a smart tag system results, allowing merchandise to be traced on the computer screen, capable of performing discriminative tasks according to the imposed regulation rules on the merchandise IDs.

Abstract: Unauthorized removal of articles e.g. from a retail store, each article carrying a read/write tag, is detected by a security system having at least one point-of-sale apparatus (30) arranged to write specific data into (or erase specific data from) the tag to indicate that the article has been paid for, and a detector apparatus (40) for the or each exit of the store and arranged to read each tag to determine if the specific data has been written into (or erased from) the tag, and otherwise to initiate an alarm. The system also includes a refunds/returns detector apparatus (50) to read the tag of each article presented to it, to determine if the specific data has been written into (or erased from) the tag, and to erase (or write in) that data so that the article can be returned to stock.