automatic identification of cycling.

Your watch can count steps, and with the step length you set it can roughly calculate a distance. On a bike it doesn't have anything to count. And, for the MoveIQ the GPS doesn't work. So, the only way to count your distance is by each time starting a Bike activity. 

You could use a simple tracker on your bike, if you want to know how much you drove your bike, as that is quite accurate ;). 

Dear Casper, thanks a lot for bothering and writing an answer. 

My bike is equipped with a pedaling frequency sensor (no real idea how to call this in English). So the trigger to start to measure could be taken from this device. Once the Fenix receives signals from this sensor it "knows" - well, I am riding my bike (depending on the ID of the sensor, it even might know, which bike..I do not know, I use it only on one bike). Next step could be (I have again not clue, if so) to switch on "automatically" the GPS and track the distance. "un"-trigger the fenix, after there has been no signal anymore from the sensor for..3 minutes?. Another way to measure the distance would be, to guess the km/turns of the pedal. This can either be set manually via "connect" or it could be measured with a special function like: go (per GPS) a certain distance from here to there and then you just divide the pedal turns by distance and thats it (average value only, of course). Another option: You calculate by turns of the pedal, how outworn your bike is, as actually the pedal turns are normally connected with a similar weight per push (otherwise you change gears) and the pushes on the pedal a probably more important to the "aging" of the bike, then the real kilometers, which is also just an asumption, that this has to do with the age of a bike. Hm. Do not know if this can work. 

It seems like you are developing a complete new device . This intelligence is not present yet, and will never be present in the Fenix 5+ as the model is seen as old, and probably impossible in other watches too... I bet there are multiple reasons you don't want to have GPS kicking in automatically, as this is killing for your battery. 

We would already be happy if the features of the 6-series would be made available in the 5plus-series, which is also not going to happen.

So, just remember starting your 'bicycle' activity when you start, and stop it when you're done, as that is the most accurate you will get.

Your sensor is probably a cadence sensor.  However it cannot be used as a trigger as the watch only searches for sensors when you are going to start an activity. I would imagine that continuously searching for sensors would affect battery life.

Ronand - but the watch identifies my mobile, when it is in reach...so it seems to "scan" the BT continuesly anyway. 

Casper - well, once my watch gets more intelligent I might not be able to catch up. At least by this way something in my environment is less intelligent than myself, so I am fine with the status. So I will keep going to gather the age of my bike by listening to the noises it makes...Cheers!