This device sends text messages when mains power is lost and also notifies you when power is restored. It also monitors the voltage of the batteries needed to power the device during a power outage.
You only need to configure the device, i.e. programming the telephone number of the cell phone that should receive the text messages. After that, you'll receive text messages whenever mains fails and when it's switched back on, as well as when the battery is low or empty.