Drive Stalker makes hard drive monitoring easy by allowing you to select any volume on a system, mark them and check regularly that it has sufficient free space and is operating correctly. Drive Stalker can be scheduled using the Windows Task Scheduler and can send an email notification when problems occur. This is a very simple but very powerful monitoring tool. In the free edition checks can only be run manually. All features are available in the full version.
Drive Stalker currently monitors for: drive status, drive not found, low drive space (by % or GB), no drive selected.