The only thing a thermometer to measure the temperature has to be reliable. And that can not the device.
I wonder how this device has been authorized as a medical device. I can not imagine. I will definitely inform about the BfArM here. A thermometer is so unreliable measures may endanger life.
To insert or change the batteries, you need a very small Phillips screwdriver. This course is not present in the package. This is far too cumbersome.
The manual is also really bad. There are several keys mentioned there and named with numbers, no one bothers to mention, however, that key is meant by what number.
I have the equipment returned, and strongly advise against purchasing.