Can the PowerCurve Sensor work with spin bikes found in gyms?

Yes and no. In order to make a correlation between speed and watts, the bicycle trainer must increase the rotation speed as the pedal force increases. Common trainers in gym don’t behave that way. A PowerCurve Sensor can be used if you can attach the wheel sensor and magnet, but power will not be accurate as it is not possible to calibrate them. The wheel circumference value will need to be adjusted for realistic speeds depending on the design of the spin bike.