The plate is a CD-ROM player cover, bent upwards to hold a clothes peg. The transmitting LED is loaded there. The 488 Hz tone is generated with the usual XTAL+divider chain that drives a 2N2222A (the metallic cylindrical "thing").
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In the center of the board there is a current generator (TO-220 transistor, the white cube, two red LEDs in place of a zener) with a jumper to provide two drive levels.
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