It has an accelerometer and two flashing modes. Slowing down by coasting or downshifting flashes the LEDs twice per second. Slowing down by braking hard flashes the LEDs five times per second. The tag is independent of the brake light, all it needs is a 12volt supply when key is on. They also sell a module that integrates the stock brake light instead of using the tag style. I put an order in. They expect deliveries around June 15. I will report when I have it as far as brightness.