SENS is an acronym for the System Event Notification Service.
On Windows XP/W2k3 SENS is baked into Winlogon - in Vista+ it is a separate service hosted by one of the svchost.exe instances on the system.
SENS is purely informational and reactive - other components subscribe to SENS notifications or send notifications about their status to SENS. Those components may in turn do something as a result of getting a SENS notification - the role of SENS is only to send and receive notifications.
Example: After the screen saver on the system is started it posts a StartScreenSaver event to SENS to indicate it has started, any other services that have subscribed to SENS notifications get notified that this SENS event has occurred.
System Event Notification Servicehttp://msdn.microsoft.com/en-us/library/windows/desktop/cc185680(v=vs.85).aspx
SAMPLE: Using ISensNetwork (SensNetDemo.exe)http://support.microsoft.com/kb/321381
You receive error 0x80240020 when you use Windows Update Web site, Microsoft Update Web site, or WSUS to install updateshttp://support.microsoft.com/kb/910341