The customer app, self monitoring, udl, signalling to arc on both WiFi and GSM. I don't use the engineer app as there is little control and management all udl is done from the office machine and logged etc I can see the engineer app having more use when it is centrally managed. Never had a report of downtime or noticed on my own system. Like the SMS over WiFi on the basic stuff. Also like how it can be pushed to an arc for more conventional monitoring