I have these. They flash alternating blue and red. They flash when there is motion and it is dark out. Both conditions must be true for it to flash.

I once had the bike in the back of my car, and when I hit a bump while driving the car, the lights would flash.

Each light takes 3 AG3 cells.

The bad English on the package is amusing. The title is "Alarm Light of Bicycle," and the subtitle is "Take not to safe!"