@DCJinWA it will wake up for the configured teams games, and give you the 5 min warning.
Once it's set up, the app is not needed - the light is connected to Bud's servers via wifi. Phone doesn't even have to be in the same country
It does go to sleep when matches aren't on, so the batteries last years generally. The test button only works when the device is awake. If you turn it on and off again manually, I think it stays awake for a few minutes.