You know how much you rely on your trusty smartphone. You know you check it a lot. But you probably tell yourself that it is all in the name of productivity and socializing, and that you have your use of your favorite device well in hand. In short, you're not one of those zombies perpetually staring at their screens, ruining their relationships, and missing out on an unmediated experience of the world.

But are you sure?

A new study suggests you might want to think a little harder about the question.

For the research psychologists out of the UK's University of Lancaster installed an app on the phones of 23 young people between the ages of 18-33 that minutely tracked exactly when they used their devices over a two-week period. The researchers discovered that a lot of us are probably seriously underestimating how much time we spend with our phones.

What would you do with an extra five hours a day?

As you might suspect from your own experience, most of the time the study subjects interacted with their phones in short bursts of 30 seconds or less. But these quick checks really added up. And it's not hard to see why -- the participants got their phones out a total of 85 times per day.

The inevitable result of all that fiddling with their phones was a tremendous amount of total time spent interacting with the devices. On average, the subjects spent five hours a day on their phones. Yes, five hours! As the research release points out, that's "about a third of the time they are awake." (Imagine what you could do if someone magically added five hours to your day.)

And the real kicker is the study participants were totally unaware of just how much time they were devoting to their devices. When asked to guess how much time they were spending looking at their phones, the participants underestimated their usage by half.

Of course, this is a tiny study with less than two dozen participants. It's also focused exclusively on young, British people. That could mean the data is skewed, or that if you're older or American you might be in the clear when it comes to wildly underestimating your smartphone usage. And, who knows, maybe the study subjects really had five hours a day of productive tasks to do on their phones. But in your heart of hearts, do you really want to bet on that?

Do you think scientists would find something similar if they monitored your smartphone for a few weeks?