This kit combines an Arduino and a 3-axis accelerometer (even though it only uses one axis) to sample the forces on one axis. When the force exceed the tolerance a digital signal is generated. By placing a relay on the digital signal, an external electronic device can be turned on and off. For this kit, the external device is an LED brake light. Some LED brake lights have enough room in the housing to fit the Arduino, accelerometer, relay and two 9-volt batteries. By packaging all this inside the brake light, it can then be mounted anywhere. It wont work as well as a light activated by a brake lever but it does work well.