The Gravity+ Tail Light has redesigned mount that works with the included seatpost and seatstay brackets. If you'd like a backpack clip compatible mount, you can find one here. 

To allow the accelerometer to calibrate, always install the Gravity+ on your bike before powering it on. Hold the power button down for 1 second to turn the light on or off. Then, keep your bike still for 1 second after pressing the power button to complete the calibration. 

DETAILS

• Automatic accelerometer brake light function shines 100 lumens bright
• 2 Modes (runtime): Solid - 20 lumens (12 hours), Flash - 80 lumens (30 hours)
• USB rechargeable li-polymer battery
• Weatherproof exterior for all season riding
• Includes brackets for seatpost and seatstay mounting
• Mounts vertically or horizontally
• Includes Micro USB recharging cord
• Weight: 1.9 oz