Mac OS X version 10.11 ('El Capitan') is not USB compatible with the GLO. To update the GLO's firmware use a Windows PC or a Mac running a version of OS X earlier than 10.11.
After updating software you may need to manually reconnect your device to the GLO. For iOS devices go to the Bluetooth menu and select your GLO. This will initiate a connection from your device to the GLO. After this initial reconnection the GLO will automatically reconnect to your iOS device.
Changes made from version 2.70 to 2.80:
Garmin Connext stability improvements
Changes made from version 2.60 to 2.70:
Add Garmin Connext support for use with Garmin Pilot app (facilitates battery state and firmware version reporting)
Changes made from version 2.50 to 2.60:
Improvements to unit update process
Changes made from version 2.40 to 2.50:
Fix missing tenths of seconds in GPS timestamp
Changes made from version 2.30 to 2.40:
Add support for four simultaneous Bluetooth connections.
Turning GLO on now requires holding down the power button for one second.
GLO will turn off automatically after five minutes with no Bluetooth connections.