The critical part of detecting an error, is notifying the appropriate person. Overseer supports notifying system administrators via Email or text message(SMS). This can be done once specific thresholds are reached. Notifications can be sent to one or more Email addresses/phone numbers, by using a notification group. Notification groups can easily be edited later to add a new person to the list that gets notified, without editing each resource.

Notifications can be sent via:

Get Email in your computer's inbox, your Android/iPhone EMail inbox while on the road, or anywhere with web access using your web mail.
Text Message
Overseer can send notifications via text message, so you get notified instantly of any issues, even if you don't check your Email constantly.

Other Notification Features:

Notification Groups
Overseer lets you tag a notification group to each resource. This enables you to define multiple people that get notified when something goes wrong with that resource. You can then easily change notification groups without having to edit each and every resource.
Notification Thresholds
Define when notifications are sent(i.e. resource down more than 10 minutes), how often(if at all) notifications are re-sent, when(and if) to stop sending notifications, and send a notification when the resource recovers.
Custom Text
Customize the subject and body of any notifications sent via Email or text message.
Notification Limits
Setup global limits per Email or cell phone#, preventing overages or floods when many resources are offline at once.
Resource Dependencies
Any resource can be configured to depend on any other resource. This prevents polling that is guaranteed to fail, and can be used to prevent excessive notifications when a critical dependent resource is down-- you can receive notification for just the critical resource, instead of every resource that depends on it as well.