What to-do with Slide in case of a power failure?
You can still open and close your curtains by hand, although Slide will forget its position if the curtains are moved when the power is off. In that case, once power is back and Slide is on, you will need to re-calibrate Slide again. This way the device can determine the length and weight of your curtains once-more to function correctly.
If you did not move your curtains during a power outage, then re-calibrating Slide is not necessary, as Slide remembers the last position it was in before power failure.