There are many ways to measure power that you generate when you cycling. When you push the pedals, all parts of a bicycle slightly deform under the load. The power from your body flows through the bike propulsion system to a driving wheel. This power produces the traction force in the contact between the wheel and the ground. The power can be measured in any element, starting from the pedals through the crank, the chain ring, the chain to the rear hub and spokes.
A real bike doesn't convert your efforts to the driving power in full. Some amount of energy disappears from the system due to energy loss in the transmission components. The actual power that you put to the road is slightly lower than the power input from your legs. On the road power reflects integrated performance of you and your machine. It is clear that the ideal performance monitoring sensor should track the watts that you need to compete and must be installed as close to the road as possible. On the other hand, for those who want to track workouts and burned calories, the power sensor installed closer to the input from the body (pedals, cranks) will be a better option.
Laser Spoke is a performance monitoring system for you and your bike. Installed on the hub of the rear wheel, Laser Spoke detects how much the hub twists relative to the rim while under load. Simply put, Laser Spoke uses the wheel, installed on your bike, as a torsional spring to measure torque and power output. This measuring performed with accurate laser system.