In order to detect power failures to your appliances (like fridges, pumps, etc.) it is enough that you plug your iSocket to any free wall socket as long as this socket located on the same electrical circuit (powered from the same breaker) with your appliance. You do NOT need to plug your appliance into iSocket, because iSocket detects mains failure - power interruptions in your wall socket. If you do plug your appliance into iSocket you need to turn it on in order to energize your equipment connected into iSocket because internal relay of iSocket is turned off by default. You do this in the 'Power Switches' section.
NOTE! Connecting your appliance into iSocket without real needs you create a so called extra point of failure. For example, occasionally you can turn it off and de-energize your appliance, or you can mess up with thermostat settings and it will be turned off, or internal relay of iSocket will fail and your appliance will be de-energized. Note about relays: they are designed for resistive loads, not for inductive. Some fridges/freezers with pumps will have surges on power on/off events and there will be inductive load that may damage relays. It is not failure of your fridge, neither iSocket. This is how fridges/freezers designed and how relays are designed too. We do NOT recommend to plug fridges/freezers into iSocket directly without real needs.
What is the "real needs" then? Well, say, you don't have any free wall outlet for iSocket on the same electrical circuit that your appliance. If you are going to plug your fridge into iSocket keep in mind that reminder about relays. Another reason why you may want to plug your appliance into iSocket is because you want to switch it on/off/reboot remotely (say, you have a router). This is absolutely fine as these are features of iSocket: remote switch on, remote switch off, remote reboot. So the main reason when your appliance should be connected to iSocket is when you plan to use these features. That is when you need 'Power Switch' feature.
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 there will be a software update in Q2 2021 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.