St. Clair Software has released Jettison 1.4.1 (http://tinyurl.com/kvonedl), an update to their Mac OS X application that automatically ejects external drives before your Mac goes to sleep.
Jettison eliminates the hassle of manually ejecting Time Machine backup drives, network server volumes and flash drives. Just close the lid of your MacBook and Jettison does it for you. Version 1.4.1 improves the logic for ejecting and remounting all disks, with specific improvements for SD cards and flash drives. It also delivers user interface refinements and support for Yosemite’s “dark mode.”
Jettison requires Mac OS X 10.6 or higher. It’s a free update for registered users. For new users the cost is US$4.95.