The Gravity Plus Tail Light has a built-in accelerometer that detects deceleration or swerving and automatically changes to a super bright, solid beam to warn following traffic. 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.
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.