Unfortunately, the RPM Speed sensor is not compatible with most spin bikes.
The RPM Speed Sensor is designed to mount on the hub of a bicycle wheel. It measures the rotational speed of the wheel and multiplies it by the wheel size to determine speed. Most spin bikes use a solid flywheel to simulate the resistance, making the RPM Speed Sensor difficult (if not impossible) to properly mount.
Additionally, even if the RPM Speed Sensor is properly mounted, the rotational speed of the spin bike flywheel is unlikely to directly equate to a standard road wheel. With that in mind, though it may sometimes be possible to receive speed data from a spin bike, challenges remain in finding the proper wheel circumference for accurate data. For these reasons, RPM Speed Sensor use with spin bikes is not recommended or supported.