Some of the Withings trackers are able to track your elevation, whether it is with an altimeter or with GPS.

Elevation with an altimeter (ScanWatch, Move ECG)

Floors climbed are tracked via an altimeter. The altimeter measures changes in atmospheric pressure (which changes as you gain or lose elevation) to track your elevation. The elevation data is available in the app, in Activity.

Elevation with GPS (Steel HR / Steel HR Sport, Pulse HR)

GPS means that when working out with your smartphone you will be able to track the elevation you have covered. Data is available in Altitude Gain in the workout details.