This Thermoter is based a low cost BLE solution,  with which we can make the final project cost <1$. there 2 temperature sensor on the board, which i drilled holes on the case to make it out, and also 2 presice  chanel for  temperature compensating  , to make the temperature output error <0.1 degree, in its testing arrange(Celsius 30 ~ 40 ).
The most important spec:

• Thin& small ... i intends to make it diameter less than 20mm, and thickness 1.6mm plus the components, same size as a 2016 battery . 
• Low cost
• Long life, > 100 days with CR2016 battery.
• Easy& confortable.