A medical sensor based on radio frequency ID tags (RFID).  In 2019, after three years of research and development, Stanford University developed a stretchable RFID sticker that adheres to the skin to monitor a person's respiration and pulse.  Temperature and sweat detection is also planned.  See 
RFID.
The BodyNet System
Using metallic ink on a rubber sticker, the RFID tag bends to the person's body.  The receiver clips to the clothing and sends out a small amount of energy that causes the sticker to emit back the data that are periodically transferred to a smartphone via Bluetooth.  (Image courtesy of Bao Lab, Stanford University.)