A mobile device (100) including a source (240) for emitting electromagneticradiation, anenclosure (430) having a side wall, and a detector (250) for detectingelectromagneticradiation emitted by the source is described. At least a portion (230) of thesidewall isadapted to transmit electromagnetic radiation from the source. The source anddetectorare positioned inside the enclosure. The detector is spaced from the source,and isarranged to detect electromagnetic radiation from the source, in use, that isreflected froman object outside the enclosure and passes through the portion of the sidewall.
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