@Andi-Buzer Here You have a garmin statement about their solution. They are using baro for this and ‘moving forward’
Garmin devices that feature a barometric altimeter sensor can determine when you are going up or down by detecting a change in air pressure which will change as you climb or descend a flight of stairs or a hill, for example. Knowing this information allows the device to give you credit towards your daily floors climbed goal.
What Are the Requirements to Receive Credit?
In order to receive credit you need to meet the following requirements:
A floor climbed is equal to 10 feet (3 meters) in elevation gain.
Consistent arm movement tied to walking as you climb.
Riding in an elevator would not earn you credit nor would riding a bike up a hill/mountain.
Stopping in the middle of climbing could result in loss of credit.
…and
I Am Not Getting Enough Credit
Credit is given for an consecutive increase of 10 feet (3 meters) in elevation with a grade of 10% or higher.
For the most accurate measurement do not hold onto the hand rail when climbing stairs.
Do not skip stairs (walking up every other stair).
When walking outdoors, the grade of the hill needs to be at least 10% which is an angle of about 6 degrees.
Remember that to earn credit towards your goal you must be moving forward and up.
Elevators: You move up but not forward.
Exercise equipment: With most equipment you do not move up or forward.
source:
https://support.garmin.com/en-US/?faq=LJ6vYF2phv7JUAOlsRRjC8