Abstract: Technologies are described herein for detecting the presence and activity of a mass storage device. A resistor divider circuit generates a voltage indicating whether a mass storage device has been mated to a mass storage backplane and whether the device is active. The circuit provides a voltage within a first range when the device is not mated to the storage backplane, and provides a voltage within a second range when the device is mated to the storage backplane but is inactive. The circuit also provides a voltage within a third range when the device is mated to the storage backplane and is active. The circuit can be connected to an integrated circuit that can determine, based on the output of the resistor divider circuit, whether the device has been mated to the storage backplane and whether the device is active.