You can request the temperature anytime when the power is presented. When the power is failed the unit will sleep. There is a small battery inside the unit so you can't monitor the temperature all the time when no power. However, we expect a software update in the future where we will add a facility to monitoring the temperature in a smart way during power outages - you will be able to configure how often the unit should wake up to probe the temperature and thresholds against which it should probe it. When it breaks thresholds you will get a notification. This way the temperature can be monitored one or two days if wake up interval is reasonable (about every hour). Probably it will be longer, we don't know - we are testing this feature and it will be release in the future with no extra fee if you already have the sensor and essential temperature option in your plan.