If you have an indoor spin bike and would like to add a power meter to it, your only option are power meter pedals. Almost all spin bikes allow you to remove your current pedals and install new ones, and therefore, you could easily attach a set of power meter pedals.
Some customers ask about other power meter types such as crankarms. Unfortunately, power meter crank arms such as 4iiii and Stages will not fit on an indoor bike as they use a different interface.
Please note, these power meter pedals require the use of road cycling shoes and 3-bolt cleats (the cleats are included with the power meter).