What is a power meter and why do I need one? So I've been looking to become a triathlete soon and I'm hearing all this talk about power meters.

Now, upon googling I found vague information which is why I came here. Exhibit A. That article gives me some sort of idea but it's not good enough, questions that remain unanswered are:


Is this another toy to measure data when you train so you know how you've trained?
Does it help in any way during a training session?
More details&hellip; how does it all work? There are heart rate zones and I'm told to run/cycle in a certain zone while training &hellip; anything similar for power meters?
Lastly and most importantly, I am a beginner/intermediate (ran a few mediocre run and cycle races).
Will a sports watch (say Garmin Forerunner 920xt with the run HRM) be good enough?
Since you say you're looking to become a triathlete soon it's far too early to be thinking of advanced training aids like power meters. 

The first few things to do (not necessarily in this order) are


join a tri club
enter a triathlon or two
join a tri training squad
observe your (comparative) strengths and weaknesses
get a well recommended triathlon book. 
use a GPS app for recording and comparing your training and race efforts (eg Strava, mapmyride)
use a heart rate monitor to help find and track your training levels


It's easy to spend lots of money in the first blush of enthusiasm, only to find later that it was wasted. 

Take it a little slower, and make sure you're getting good advice. When talking up a new sport it's easy to go about it the wrong way and cause early injuries, or develop poor habits or techniques that cause long term problems. This applies to all three triathlon legs. 

In the case of the cycling leg, you need to get cycling advice from a seasoned triathlete. Triathlon cycling is quite different to normal road racing, especially as the distances increase. You'll be trying to avoid using the muscle groups that provide the drive for the run leg, using a much lower cadence than a roadie would, and using a different bike. 

The time to consider a power meter is when you're at the stage where you have a training bike and a race bike, and both are worth more than your car.