Cycle trainer manufacturers Kinetic are set to release a Bluetooth Smart system that can provide you with power readings from Kinetic fluid trainers.
The product is called the Kinetic inRide Watt Meter, and consists of a heart rate monitor, a power sensor that attaches to the rear of the trainer, and an iPhone 4S app you can also run on an iPad 3. The sensor measures speed and cadence at the tyre and converts it into power. Calibration is done on the fly via a coast down, which keeps things simple.
Kinetic say that their "incredibly accurate fluid trainer power curve allows precise wattage readings at exact speeds". From experience we know that getting turbo trainer power to match measured power (from an SRM, PowerTap or similar, for example) is not easy. Roller resistance and heat build up and can cause errors and drift. With this in mind, we hope to test the inRide in the coming months.
The inRide App turns your phone into a cycle computer with a number of useful functions: power (current, average and max), heart rate (current, average and max), speed, cadence, distance, time-in-zone for heart rate and watts, programmable rider data for training zones and calories burned (this should actually be derived directly from power).
You'll also see various power metrics such as training stress score, nPower, iFactor and mean maximal power across five durations. It's designed to be easy to upload your workouts to training websites.
Kinetic say the advantage of using Bluetooth Smart is that it "eliminates additional phone dongles and cross-talk with other devices". It also shouldn't drain your battery too quickly.
Kinetic have priced their system at £175/€199/$US229 (not including the trainer). It's compatible with the Kinetic Road Machine, Rock and Roll and Pro Trainer and should be available from September 2012.
The power sensor attaches to the bottom of the trainer