Long ago I worked at a company which will remain nameless, we had a cellular modem for sending SMSs if anything went wrong. It worked well, didn't need the internet to function, notifications were almost immediate. The problem was the box was in the same datacentre as all the equipment. the whole district lost power, the UPSs ran dry, the backup generators failed and so when the power went out we were not alerted as there was no external monitoring. The first we knew was arriving in the office and customer support were screaming. It was rather, er, awkward to have been so unaware. It wasn't that we could have done anything, flying over to the datacentre wouldn't have achieved anything of course. Meanwhile the merchants using the service would have lost tons of cash. Needless to say, we set up more monitoring systems after that ;-)