AFAIK, Azure only alerts when a threshold you specify is reached. For instance, you set a budget of $10k and you specify 50% threshold. So when you have consumed $5k, Azure will send you an alert. However, suppose your daily run due to some bad selection is $400, in this case, Azure will tell you only on the 14th day that you've consumed 50%. On the other hand, CloudAlarm doesn't need threshold – it just takes your budget and see whether your daily burn rate estimates to exceed your budget. In the above example, CloudAlarm can thus notify you on the 2nd day itself because $400 * 30 is $12k.
Yes, CloudAlarm, as of now, depends on Azure's pricing data API to do this calculation. It's easy for Azure to do what CA is doing but their threshold based design is a problem, which only prompted me to create this service.
CA also has 'new resource' alarms as well, which are almost instant (a few mins after creation of a new resource), which helps you monitor and fix resource created with unexpected, expensive tiers. This can often happen with automated creation of databases, for example.
I just did it because Azure wasn't doing it, despite people complaining, including me, had faced multiple such issues of unexpected expensive resource got created without intention/knowledge.
