I made this little tool a few days ago to help me keep track of the bitcoin/USD price since it has been so volatile. I was going to wait a few more days and polish up the site before making a HN post, but given how bitcoin is tanking hard right now I think it's an appropriate time to release.

Currently it supports alerts based on fixed $ movements and % change of price over time. Let me know what you guys think and if there are any features that I should add!