In the event of a power cut, all mains powered devices have built in back-up power sources.
Both the Sensor and Sensor+ operate on battery power and so would not be affected by a power cut, capturing and storing data regardless.
Should the Sensors be unable to communicate with the Hub (i.e. due to power outage or being out of range of the network) then they can store 1-5 days worth of data (dependent on Sensor type and its configuration).
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