Thanks! This was actually my motivation to build it, Bitcoin sometimes can be very volatile and within a short time its value can change substantially.

Currently I'm making use of the data provided by BitcoinAverage, because the market is shared between a few exchanges.

In the future I may implement custom alerts, but I don't see them as a very interesting feature. What I'm working on is on a system that actually detects itself when there's the chance of a substantial decrease in value.