Some smart trainers also give the option to connect to the power meter (ANT+ Power) of the trainer:

The power meter is not smart and does not simulate the slope of the road. If one wants the smart trainer to simulate the slope of the road, then one should pick ‘smart trainer’ instead. When the smart trainer is picked as input for speed, one will automatically see ‘Open Road’ also pick the smart trainer to control the resistance/grade:
