Abstract: Infrared stationary lens systems for performing multi-dimensional scans of scenes are provided. Systems illustratively include a stationary lens, a first scan mirror, a second scan mirror, and at least one actuator. The stationary lens transmits infrared light and has an optical axis. The first scan mirror has a first axis and pivots about the first axis to direct images of a scene to the stationary lens along a first dimension. The second scan mirror has a second axis and is located in an optical path between the first scan mirror and the stationary lens. The second scan mirror pivots about the second axis to direct images of the scene to the stationary lens along a second dimension. At least one actuator controls the first and the second scan mirrors such that the first and the second scan mirrors step and stare across the multi-dimensional scan of the scene.

Abstract: An imaging device including an element having at least a reflective sphere portion wall, a converging lens, and an image detection array, wherein the lens and the array are fixedly assembled with respect to each other on a mount, said mount being hinged with respect to said element.

Abstract: A device for evaluating the appearance of the surface of a tire (P) comprising a color linear camera (1) comprising means (14, 15, 16) for separating the light beam (F) reflected by the surface of said tire (P) and entering the camera (1) into at least two base colors (R, G, B) of given wavelength, so as to direct the light beam to as many sensors (11, 12, 13) capable of obtaining a basic image in gray level (41, 42, 43) for each of the base colors, as many lighting means (21, 22, 23) as base colors, said lighting means being oriented so as to light the surface to be evaluated at different angles, characterized in that each of the lighting means (21, 22, 23) emits a colored light (R, G, B) that differs from that of the other lighting means, and the wavelength of which corresponds substantially to the wavelength of one of the base colors selected by the camera.

Abstract: Systems and methods disclosed herein provide for some embodiments infrared camera systems for maritime applications. For example in one embodiment, a watercraft includes a plurality of image capture components coupled to the watercraft to capture infrared images around at least a substantial portion of a perimeter of the watercraft; a memory component adapted to store the captured infrared images; a processing component adapted to process the captured infrared images according to a man overboard mode of operation to provide processed infrared images and determine if a person falls from the watercraft; and a display component adapted to display the processed infrared images.

Abstract: A portable camera system (100) includes a lens (104) for forming a focused image of a survey scene (106) onto a focal plane array (108). The focal plane array (108) comprises a cooled two dimensional array of quantum well infrared photo detectors, (QWIP) having a peak spectral responsivity in the wavelength range of 10.4 to 10.8 ?m. The camera includes a cooled band pass optical filter (110) having a peak spectral transmittance approximately centered at a wavelength of 10.57 ?m and a full width half maximum spectral transmittance bandwidth of approximately 10.3 to 10.7 ?m. The camera system (100) is usable to detect an invisible gas plume in a video image of a survey scene if the gas plume contains sulfur hexafluoride (SF6), ammonia, (NH3), Uranyl Fluoride (U2O2F2), or any other gas having an absorption band that that at least partially falls within the wavelength band 10.3 to 10.8 ?m.

Abstract: A night vision system and method for imaging an object at or near room temperature and in the wavelength region up to 2.5 microns is described. The includes a photodetector having a cut-off wavelength of 2.5 microns under the room temperature, an optical system configured for collecting light and focusing the collected light onto the photodetector, and a spectral filter located in an optical path of light propagating toward the photodetector. The spectral filter is configured and operable to selectively filter out light of wavelength shorter than a predetermined value, thereby gradually shifting operation of the night vision system from mostly reflection mode to a combined reflection and thermal mode, to allow the night vision system to detect light reflected from and emitted by the object being imaged.

Abstract: An apparatus and method for characterization of a directed beam of electromagnetic radiation is provided. An exemplary embodiment of the invention can include an apparatus and measuring technique method which uses a model for blackbody radiation that includes consideration all the degrees of freedom due to translation, vibration, and rotation of molecules or atoms that make up the absorber and a heat transfer term which averages the behavior of all the atoms of the material as a function of temperature. This apparatus and method provides an advantage of increased accuracy, substantial reductions of time required for processing, simplification of measuring processes, and reduction required equipment.

Abstract: A method for detecting unknown materials, such as drugs. A first location is surveyed using a video capture device to identify a second location comprising an unknown material. The second location is interrogated using SWIR spectroscopic and/or imaging methods to generate a SWIR hyperspectral image. The SWIR hyperspectral image is analyzed to associate the unknown material with a known drug material. A system for detecting unknown materials, such as drugs comprising a first collection lens for collecting interacted photons from a first location and a visible imaging device for generating a visible image. A second collection lens may collect a plurality of interacted photons from a second location and a tunable filter may filter the interacted photons. A spectroscopic imaging device may detect the interacted photons and generate a SWIR hyperspectral image. A processor may analyze the SWIR hypespectral image to associate an unknown material with a known material.

Abstract: A solid-state imaging device is provided. The solid-state imaging device includes a plurality of arrayed pixels, an optical inner filter layer, and a light-blocking side wall. The plurality of arrayed pixels each includes a photoelectric conversion portion and a pixel transistor. The optical inner filter layer is provided for blocking infrared light and formed facing to a light-receiving surface of the photoelectric conversion portion of a desired pixel among the arrayed pixels. The light-blocking side wall is formed on a lateral wall of the optical inner filter layer.

Abstract: A network of controllers for controlling and monitoring associated assay testing systems coupled to a remote monitoring unit for monitoring and controlling the controllers and/or the assay testing systems is disclosed. Each controller transmits a display image representing the status of the respective assay-testing system. The remote monitoring unit automatically detects if the number of display images from the controllers is greater than a threshold number of displayable, static thumbnail images and, when the threshold is exceeded, displays thumbnail images dynamically in a scrolling or streaming motion. The thumbnail images, whether static or dynamic, are updated in real-time or pseudo-real-time to reflect updated status of the assay testing systems.

Abstract: Methods and apparatus for monitoring a temperature of an object over time using a thermal imaging camera. The methods and apparatus may gather infrared temperature data from a selected source of temperature data within a scene at a selected time interval and display a graphical plot of the gathered temperature data on a digital display.

Abstract: A portable electronic device includes a digital imaging subsystem with a lens having an optical axis. A case encloses and supports the digital imaging subsystem in a first defined positional relationship to the case. A removable panel is coupled to the case and held in a second defined positional relationship to the case that covers the digital imaging subsystem without the removable panel being directly connected to the digital imaging subsystem. An optical component is supported by the removable panel such that the optical component is aligned with the optical axis and alters optical characteristics of the digital imaging subsystem. The device may include a power supply and an electronic control system coupled to the digital imaging subsystem and the power supply enclosed in and supported by the case. Electrical connectors may couple the power supply and the electronic control system to an electrical component on the removable panel.

Abstract: A photographing control method is provided. The photographing control method includes capturing an image of an object, detecting a facial area from within the captured image of the object, adjusting a location of the photographing apparatus based on a location of the detected facial area, and adjusting a zooming state of the photographing apparatus so that a size of the detected facial area falls within a predetermined size range.

Abstract: A dual band imager includes a lens to receive short wavelength and medium or long wavelength radiation from a scene to be imaged, a beam splitter positioned to receive the radiation from the lens, a medium or long wavelength to short wavelength image converter positioned to receive long wavelength radiation reflected via the beam splitter and to transmit the image information via short wavelength radiation, and a detector to receive the short wavelength radiation containing the image information through the beam splitter or from the scene and from the image converter.

Abstract: The present disclosure relates to combination of images. A method according to an embodiment comprises: receiving a visual image and an infrared (IR) image of a scene and for a portion of said IR image extracting high spatial frequency content from a corresponding portion of said visual image. The method according to the embodiment further comprises combining said extracted high spatial frequency content from said portion of the visual image with said portion of the IR image, to generate a combined image, wherein the contrast and/or resolution in the portion of the IR image is increased compared to the contrast and/or resolution of said received IR image.

Abstract: Apparatus, systems, and methods autonomously detect a chemical plume. The system includes an apparatus for splitting a beam of electromagnetic radiation and feeding the split beam to at least two detectors, which are operably connected to a first bandpass filter and a second bandpass filter that passes a wavelength of electromagnetic radiation that is similar in magnitude but offset from the wavelengths passed by the first bandpass filter. The system further comprises an analysis system configured to analyze images from the at least two detectors, a processor, and a non-transitory, computer-readable medium comprising code configured to direct the processor to perform functions. Exemplary functions include comparing a plurality of deterministic features, a plurality of probabilistic features of objects, or both, from the at least two detectors and determining if a difference between the compared images represents a chemical plume.

Abstract: In an infrared image capture device, an infrared optical system (10) has an objective optical system (13) that includes a primary mirror (11) and an auxiliary mirror (12) disposed to face each other along an optical axis (AX), and forms an intermediate image of an object (not illustrated) by sequentially reflecting the infrared ray from the object using the primary mirror (11) and the auxiliary mirror (12), and a non-transmitting portion (12f) which does not transmit the infrared rays from the object exists in the center portion of the auxiliary mirror (12). The non-transmitting portion (12f) in the center portion of the auxiliary mirror (12) is formed in a concave surface which satisfies a following conditional expression (1): L/1.2<R<1.

Abstract: A handheld thermal imager includes a housing defining a cavity. A lens barrel has a first end portion and a second end portion. The lens barrel is at least partially disposed within the cavity. A lens is coupled to the lens barrel first end portion. A resilient buffer member supports the lens barrel within the cavity. A thermal sensor is coupled to the lens barrel second end portion. A processing module receives signals from the thermal sensor. A display is coupled to the processing module for displaying a temperature characteristic of a scene.

Abstract: This disclosure describes antenna elements, terahertz detector arrays formed by antenna elements, and dual-mode terahertz imaging systems that operate using terahertz detector array(s). The antenna element includes a horn receiver configured to collect radiation and capture the radiation using an antenna positioned in or proximate to a throat of the horn receiver. The antenna element also includes antenna posts electrically coupled to the antenna and extending through irises in a conducting ground plane and conductive traces electrically coupling the antenna posts to an antenna load. In addition, the antenna element includes a bolometer mounted on a first substrate, where the bolometer is electrically isolated from the antenna load and in thermal contact with the antenna load. The antenna could include a bow tie antenna having first and second arms on a first surface of a second substrate, where the ground plane is on a second surface of the second substrate.

Abstract: An infrared imaging sensor compatible with 2nd Generation Forward Looking Infrared (FLIR) Horizontal Technology Integration (HTI) B-Kit based sensors. In one example, the infrared imaging sensor includes a set of refractive opto-mechanical modules, including an afocal optical module, a receiver assembly, and backward- and forward-compatible electronics modules. The afocal optical module is configured to provide a plurality of different fields of view for the infrared imaging sensor. In one example, the sensor is configured for MWIR and LWIR imagery.

Abstract: An image sensing system includes an IR notch filter configured to block transmission of spectral energy having wavelengths in an interface region between the visible and the invisible spectra and enable transmission of spectral energy having wavelengths in at least the visible spectrum and the near-infrared (IR) spectrum, a digital image sensor including a two-dimensional array of pixel elements and configured to generate output signals at each pixel element as pixel data representing an image of a scene, and a color filter array including a two-dimensional array of selectively transmissive filters superimposed on and in registration with the two-dimensional array of pixel elements. The color filter array includes a first group of selectively transmissive filters disposed to transmit spectral energy in one or more colors of the visible spectrum and a second group of gray color filters disposed to transmit spectral energy in at least the near-infrared (IR) spectrum.

Abstract: The present invention discloses a system for identifying a human face, which includes a visible light camera, an infrared (IR) camera, a non-contact temperature sensing device and a processing unit. The visible light camera and the IR camera aim at a same photograph zone for respectively photographing at least one visible-light picture and at least one IR picture. The non-contact temperature sensing device senses a present target temperature in a temperature sensing zone, which is in the photograph zone. When the processing unit detects that a human face is existed in the corresponding zone of the visible-light picture and that of the IR picture, it determines if the present target temperature is in a body-temperature range. When the present target temperature is in the body-temperature range, the processing unit determines that the human face detected in the corresponding zone is an alive human face.

Abstract: Disclosed is a portable low-power audio-visual (A/V) device including: a housing enclosing a computer board, a projector, a speaker, a power supply and optionally a webcam. The power supply may be one or more power converters connected to a DC battery. The A/V device may include a user interface enabling web browsing with functions including scroll, refresh, home, listing playable/viewable files, and generating a projection screen keyboard. Navigating on the screen can be achieved by a user input system that is calibrated to be used on a projected image, such as an infrared point source.

Abstract: The present invention relates to a thermal vision countermeasure system to enable concealment of objects from identification by thermal imaging night vision systems, including a screen made of thermoelectric modules, disposed between the target object and an IR detector. The screen, formed of at least one thermoelectric unit, is coupled to the target object, and the thermoelectric unit includes a Thermoelectric Cooler (TEC) module coupled to a plate formed of a material selected from aluminum, copper, or aluminum with copper, the plate being substantially larger than the TEC module.

Abstract: Systems and methods for detecting a live human face in an image are disclosed. The methods and systems are capable of receiving multispectral image data that includes a human face. The multispectral image data can comprise visible light image data and near-infrared (NIR) image data. The multispectral image data can be processed to detect the human face. The detected human face in the visible light image data can be associated with the detected human face in the NIR image data to determine whether the detected human face is a live human face.

Abstract: An image processing apparatus including an image acquiring unit to acquire a first image including color information and a second image having a spectral band wider than that of the first image and a noise reduction unit to extract edge information from the second image and to reduce noise of the first image based on the extracted edge information.

Abstract: A mark which at least reflects or radiates invisible light of predetermined wavelength other than visible light is added in a space of the real world. A camera apparatus comprises image capturing means for capturing a real image in which an invisible-light image may be discriminating. An image processing apparatus, comprises: mark discriminating means for discriminating at least one condition of a position of image of mark in the captured real image, a orientation of the mark, and a distance from the mark to the image capturing means, and overlaying condition determining means for determining, in correspondence with the discriminated condition, a overlaying condition which is at least one of an overlaying position which is a position of the image of the virtual object overlaid on the captured real image in the real image, an orientation of the virtual object which the image of the virtual object indicates, and a distance from a view point of viewer, of the image of the virtual object.

Abstract: A housing for an infrared camera module may be implemented with a substantially non-metal cover configured to substantially or completely enclose various components of an infrared imaging device. A metal layer may be disposed on various interior and/or exterior surfaces of the cover. Such implementations may be used to reduce the effects of various environmental conditions which may otherwise adversely affect the performance of the infrared imaging device. In addition, one or more conductive traces may be built into the housing and/or on interior surfaces of the housing to facilitate the passing of signals from components of the infrared imaging device such as infrared sensors, read out circuitry, a temperature measurement component, and/or other components. One or more fiducial markers may be provided to align various components of the infrared camera module during manufacture.

Abstract: Full-color images of low-light scenes are generated by the systems and methods described herein using only two light channels. An array of photosensitive pixels includes two sets of pixels, the first sensitive only to light associated with a first light channel, the second only to light associated with a second light channel. Thus the first set of pixels generate a first set of electrical signals in response to incident light within the first light channel, and the second set of pixels generate a second set of electrical signals in response to incident light within the second light channel. An image processor receives the first and second sets of electrical signals and generates a full-color image of the scene by processing only signals generated by the first and second sets of pixels.

Abstract: Signal detection and recognition employees coordinated illumination and capture of images under to facilitate extraction of a signal of interest. Pulsed illumination of different colors facilitates extraction of signals from color channels, as well as improved signal to noise ratio by combining signals of different color channels. The successive pulsing of different color illumination appears white to the user, yet facilitates signal detection, even for lower cost monochrome sensors, as in barcode scanning and other automatic identification equipment.

Abstract: There is provided an imaging device including an image sensor that performs photoelectric conversion on subject light to generate an image signal, a photographing optical system that forms an image of the subject light on the image sensor, and a first optical member that transmits the subject light incident on the image sensor via the photographing optical system. The first optical member changes transmittance of a first band of the subject light according to an angle with respect to an optical axis of the photographing optical system.

Abstract: A camera producing visible light images with thermal data. The camera may include visible light lens and sensor, an infrared light lens and sensor, and a display. The display displays some of the visible light image and thermal data from the respective sensors. The visible light image is divided into an array of zones where each zone may provide thermal data associated with the corresponding portion of the target shown in the zone. The camera may sense infrared images also provide audible alarms where the alarm is emitted with a tone of variable output to indicate the relative level of the alarm.

Abstract: An infrared thermal imaging system includes a focal plane array (FPA) of infrared detectors, read out integrated circuitry (ROIC) operatively coupled to the FPA, and a microcontroller having at least one video display interface operatively coupled to the ROIC. The FPA is configured to generate an output signal in response to infrared radiation impinging upon the infrared detectors. The microcontroller is configured to send data to the ROIC via the at least one video display interface, the data including non-uniformity correction terms for correcting non-uniformities of the FPA.

Abstract: Embodiments of the invention relate to an IR camera for capturing thermal images of an imaged view, the IR camera comprising an IR camera display configured to display the captured thermal images to a user of the IR camera; a display control unit configured to control the IR camera display to further display a current temperature range of the IR camera. The IR camera is characterized in that the display control unit is configured to determine an indication scale comprising the entire current temperature range of the IR camera wherein equally sized temperature intervals have different geometric size in the indication scale based on upon the actual image content of the captured thermal image, and control the IR camera display to display the indication scale to a user of the IR camera. Embodiments of the invention further relate to a method for use in displaying captured thermal images of an IR camera and a computer-readable medium encoded with executable instructions for the same.

Abstract: Methods for comparing infrared image data and/or for generating infrared image comparison data are provided. In one method two image data sets are selected including visual-light and infrared image data from one or more points of view of a scene. Visual-light image data from each data set can be compared to determine an alignment correlation between different points of view for the visual-light data. The alignment correlation can then be used to correlate infrared image data from each data set. The correlated infrared image data can be compared to generate infrared comparison image data. Thermal imaging cameras capable of performing such methods are also provided.

Abstract: A camera module includes: a lens unit including a casing portion and a lens; and a substrate portion on which an image pick-up element is mounted. The camera module is assembled in combination of the lens unit and the substrate portion in an arrangement in which the lens and the image pick-up element are opposed to each other. The substrate portion includes: a first substrate including one of surfaces on which the image pick-up element is mounted; an infrared filter supported on a light receiving face of the image pick-up element; and a second substrate supported on a surface of the infrared filter which is opposed to the lens. The second substrate includes an opening portion disposed in alignment with the infrared filter so as not to intercept an incident light. A circuit component is mounted on the second substrate.

Abstract: Provided is a method which minimizes power consumption by controlling power of a camera that is used for recognizing a user's gesture, in a video processing apparatus, which recognizes the user's gesture and is controlled according to the recognized gesture, such as a TV or a monitor. In the present invention, a camera is driven in a low power mode or a high power mode, and when a user's specific gesture is detected in the lower power mode, the camera is switched to the high power mode for recognizing a detailed gesture.

Abstract: An imaging device includes pixels configured to sequentially output image signals for an infrared radiation having a first wavelength, an infrared radiation having a second wavelength and an infrared radiation having a third wavelength. A first pixel has the sensitivity to a first color of a primary color and outputting a first signal in response to reception of the infrared radiation having the shortest wavelength of the first wavelength, the second wavelength and the third wavelength. A second pixel has the sensitivity to a second color of the primary color and outputting a second signal in response to the reception of the infrared radiation having the shortest wavelength. A discriminating circuit is configured to compare the first signal and the second signal with each other to discriminate a reception timing of an infrared radiation having a selected wavelength in response to a relative sensitivity ratio.

Abstract: An imaging device (100) for acquiring and displaying images in real-time, the imaging device comprising i) an imaging sensor (110) comprising a radiation sensitive array (120) for acquiring an image (142), ii) a readout circuit (140) connected to the radiation sensitive array for reading out the image, iii) a signal processor (160) for processing the image for obtaining a processed image (162), and iv) a display (180) for displaying the processed image, the radiation sensitive array being arranged in rows of sensor pixels and the display being arranged in rows of display pixels, and wherein the readout circuit is a rolling shutter circuit for sequentially reading out the rows of sensor pixels for sequentially providing subsets of pixels, the signal processor is configured for, on availability of one of the subsets of pixels, processing the subset of pixels for providing a processed subset of pixels, and the display is configured for, on availability of the processed subset of pixels, displaying the processed

Abstract: Improved low light vision and thermal imaging devices are provided. The devices of the present invention employ thermionic or thermotunneling cooling, with or without Avto Metals™, to ensure efficient operation under conditions of low illumination or the complete absence of illumination to detect emitted or reflected infrared and visible light radiation, significantly reducing thermal noise to produce superior image resolution and sensitivity within a small, lightweight footprint that will have a wide range of military, law enforcement, civilian, and other applications.

Abstract: In an A/D conversion circuit and an imaging device, an upper counter acquires a first upper count value by performing counting using one output signal, which constitutes a first lower phase signal output from a delay circuit, as a count clock. After values of bits constituting the first upper count value are inverted, the upper counter acquires a second upper count value by performing counting using one output signal, which constitutes a second lower phase signal output from the delay circuit, as a count clock, and further performing counting based on an upper count clock output from a lower counter. A modification unit modifies a logic state of a count clock to a predetermined state when the count clock of the upper counter is switched.

Abstract: A system and method for optimizing fixed and temporal noise in an infrared imaging system. The system may use correction tables with correction factors, each correction factor indexed to a plurality of system parameters.

Abstract: This disclosure relates in general to the field of visualizing, imaging and animating groups of images, and annotations in IR-cameras. Various techniques are provided for a method of managing IR image data on a group level. For example, the method may comprise; capturing an IR image comprising temperature data representing the temperature variance of an object scene; storing the IR image as a first data item in a predetermined data structure; storing a second data item in said predetermined data structure; and associating in said data structure the first and the second data item such that an operation is enabled on the first and the second associated data items jointly as a group of data items.

Abstract: A system and method of identifying and locating one or more targets includes capturing one or more frames and recording position data for each of the frames. Each of the frames comprises a plurality of at least three different types of infrared image data. Each of the targets is identified and a location is provided based on the three different types of captured infrared image data in each of the frames and the recorded position data.

Abstract: A face camera mount structure in a vehicle has a camera for imaging a driver's face being disposed on a reverse side of a dial at a portion that does not interfere with a speedometer design portion on the dial. A camera facing portion of the dial that faces a lens of the camera is covered with a print of a near-infrared light passing ink that selectively passes a near-infrared light. The high transparency factor of the near-infrared light through the ink makes it possible for the camera to image a sufficiently bright near-infrared light image without being recognized by a driver of the vehicle.

Abstract: What is disclosed is a novel system and method for determining the number of objects in an IR image obtained using an IR imaging system. In one embodiment, a total of N intensity values are collected for each pixel in an IR image using a IR imaging system comprising an IR detection device and an IR Illuminator. Intensity values are retrieved from a database which have been estimated for a plurality of known materials, such as skin and hair. A classification is determined for each pixel in the IR image using either a best fitting method of a reflectance, or a correlation method. Upon classification, a total number of objects in the IR image can be determined. The present system and method finds its intended uses in of real world applications such as, determining the number of occupants in a vehicle traveling in a HOV/HOT lane.

Abstract: There is disclosed a method, arrangement, and computer program product for correcting distortion present in an image captured using an infrared (IR) arrangement, the method for an embodiment comprising: capturing a first image using a first imaging system comprised in said IR arrangement; and correcting image distortion of the first image based on a pre-determined distortion relationship. According to embodiments, the method may further comprise capturing a second image using a second imaging system comprised in said IR arrangement, wherein: said distortion relationship represents distortion caused by said first and/or second imaging systems of said IR arrangement; and said correcting of image distortion of the first image comprises correcting image distortion with relation to the second image based on said pre-determined distortion relationship, wherein the distortion relationship represents distortion caused by said first and/or second imaging systems.

Abstract: A system and method for sampling multi-spectral images of a dynamically changing scene facilitates independently dynamically adjusting the exposure of a photosensor based on a first group of sequences of images, while disregarding a second group of sequences of images, where each sequence of images is of a distinct color of light. In addition, the current description presents an innovative technique for constructing a multi-spectral image of a scene based on individually contrast-enhanced images of the scene. Applications include video photography and high quality true color stills camera with separate sensor arrays for each color channel. The control of the present embodiment can be used to produce photographs with truer color than conventional techniques.

Abstract: Provided is a light-emitting device control system, comprising a beam steering mechanism that directs a beam of light at a first surface location, wherein an illumination region is formed at the first surface location in response to the directed beam of light, a sensor that recognizes a hand gesture at the illumination region; a processor that converts data related to the hand gesture into a command signal, and a controller that instructs the beam steering mechanism to move the illumination region to a second surface location in response to the command signal corresponding to the hand gesture.

Abstract: An audio system comprises a headset comprising a pair of earpieces positionable with respect to the user's ears so that, in use, the user is inhibited from hearing sounds from the user's environment, at least one of the earpieces having a transducer for reproducing sounds from an input audio signal; a microphone for generating a captured audio signal representing captured sounds from the user's environment; a detector for detecting the presence of any of a set of one or more characteristic sounds in the captured audio signal; and a controller operable to transmit sounds from the user's environment to the user in response to a detection that one or more of the set of characteristic sounds is present in the captured audio signal.