So I purchased 2 of these units on eBay [I think I paid $30-ish each ... the ~$150 "normal" price tag is crazy] to tear one down to see what they used for the BLE comms. Unsurprising that they used the NRF51822 (QFAA H0 - Rev 3 Si) ... what was curious was the use of the AFE4400 from TI. If the development company had used a different sensing element (say an Si114x series from Silicon Labs), they would have had a less-expensive / less-complicated straight forward design. Oh well, they didn't ask us.  
 
 
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Here is the basic photodiode-with-2-wavelength-leds setup... 2 LEDs to generate the 2 different wavelengths for pulse oximetry. One LED emits visible red light (typically around 600nm), and the other LED emits near infra-red light (typically around 900nm). Interesting that they appear to use a thermistor to see if the sensor is still on the child's foot.  
 
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And, this is what is typically used in a hospital environment (sans finger wrap) ... The LEDs are contained within one package shown on the left (as you forward bias the device, you get one wavelength, and if you reverse bias it, you get the other). 
 
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