You can monitor three web sites from the free version.
The app alerts by creating a notification on your phone, and/or by sending an SMS to phone that you can configure.
You can configure your test frequency as 5 minutes, 10 minutes or any multiple of 5 minutes.
In order to relieve you from the repeat alerts, you can set a "backoff" to avoid notification on the same event for "n" cycles.
Disclaimer : Due to network conditions, occasionally a response from the server might not reach your device in time, leading to false positive ( declaring the server as down).