Originally Posted by ColaJacket

I'd add that for a beginner, a smartphone with a ride tracking app (e.g. Strava, MapMyRide) should suffice in the beginning. If you get a HRM, Power Meter, or Cadence monitor, then you might need to upgrade. Also, the dedicated cycling computers are designed so that you can constantly see the data, but with a smartphone, you probably just want to look at the information at stops or at the end of the ride, because if you keep the screen up, it will drain the battery pretty quickly. Also, if you're doing rides over 4 hours, a smartphone might need to be recharged sometime during the ride. But most beginners don't do 4 hour rides for a while.

Pro cyclists trained for decades without a computer or smartphone.

GH