@ Draco
Du hast Recht.
Es sind LEDs, Infrarot-Leds.
Hab das hier gefunden:
The Buddy digital egg monitor consists of a body (containing a battery,
monitor, and computer chip) and a measurement chamber (Fig 1). The round
pole of the egg is placed on a rubber ring over a centered light sensor
(Fig 2). The infrared light source is located at one side of the
chamber. When the chamber is closed, the infrared light is directed on
the egg and passes through its contents. During every pulse in the
embryo, the infrared light is absorbed by embryonic blood to a varying
degree; the net amount of infrared light passing through the egg is
detected by the sensor. Thus, the degree of light absorption is an
indirect measure of the heart rate.