My scale is talking to me.

Not out loud, of course, but loud enough.

All scales have something to say. They have an essentially judgmental nature. Every time you pass by, they're whispering sweet words of encouragement or making quiet accusations. Which is why I haven't lived in a house with a scale for the past 30 years. But I have one now, and it's a hell of a chatterbox.

This one's a black plastic square, 13x13, about the size of an old vinyl LP sleeve. But it is in no way analog. Sleek and black, with an all-knowing aluminum eye dead in the center, it glistens darkly in the first rays of dawn, already sharing information. About me. It knows me better than I know myself, and it wants the whole world to know it.

The scale talks with my phone and with my iPod. It gabs with a little device I wear on my hip, a lovable but demanding thing that's always crying out for attention. And both of them are in continuous contact with a website that emails me every once in a while to let me know it's up to date on how much I've been eating (calories in!), how many steps I've taken (calories out!), and how many glasses of bourbon I've sipped (At your present rate, you will weigh...Listen, maybe it's time for a talk). It even watches me sleep. These devices work in concert to capture my life, quantify it, and improve it, though, technically, that last bit is up to me.

This is a strange little arrangement I've entered into, sharing my body so freely with this consortium of processors, and I'm not entirely comfortable with it. I've digitized my life for a reason: to make peace with a world of numbers I've run from for far too long, and to take some control of that world. Except I worry that everything's been turned upside down – that I'm the one being controlled.

Looking down at the plastic clip currently begging to be held (and this is no metaphor – it's flashing the words hold me as I write), I wonder if this gadget has become something not quite inanimate. I'm no longer sure if I've entered the world of numbers or if they've entered me. And as I pick up the little black clip, it occurs to me to ask: Who is holding whom?I'm 48, and my wrestling match with my metabolism has gone on for 17 years. Early victories gave way to losses after I turned the corner on 40, but I battled back and for the last half decade it's been a hard-fought draw. During that time, I've weighed 195 or so, but at 6-foot-1, I've carried it pretty well. Still, my body mass index consistently put me just north of normal whenever I plugged the numbers into one of those online calculators. And if you haven't calculated your BMI recently, just north of normal is also known as "overweight."

BMI has its limitations, especially for athletes who pile on sheets of lean muscle, but for most of us, it's a reliable indicator. To give you an idea of the calibration, Iggy Pop's BMI is approximately 22.4, solidly in the "normal" range of 18.5 to 24.9. John Candy's when he died was around 41.2, above the "obesity" line of 30. Mine was 25.7, a mere 0.8 into "overweight" territory, but when you spend 17 years working out three days a week and watching what you eat and still come up a tiny bit overweight, it gets on your nerves.

Or it would, if I'd really been working out three days a week and watching what I ate. But routine breeds boredom, and over time my virtuous schedule had slipped. Now a good week meant I was in the gym once for strength training, and spinning once or twice for cardio. I had no idea what my diet was anymore, other than delicious.

And so, thinking there must be some fitness equivalent of Google Maps, I load up on tech and dive into the world of numbers. I start with the Withings Body Scale. It's a smart scale – WiFi enabled and digital, and it not only calculates my weight but also uses a low dose of electricity to suss out my BMI and fat mass – and it's designed with the minimalism Steve Jobs bequeathed to the world. Setup is simple enough, and so is the way it works: Step on the scale and a tiny electric current goes through your feet, up to your head, and back to the scale. Fat slows it down. Now Withings knows your insides and will use your WiFi network to send the results to your computer and an app on your phone. Over time, the numbers are graphed into a clear picture. In keeping with the new age of social media (and the old traditions of shame as motivation), you can also tweet the results of every weigh-in, though this feature is mercifully disabled on startup.

Withings wants me to weigh in once or twice a week at the same time, before I've had anything to eat or drink, but tonight I step on just to see how it works. Success is instant: I've set up my starting weight at 195, but I weigh 193. I've just lost two pounds! My BMI is 25.6, just 0.7 north of where I want it. I have my first goal. It will not be my last.Withings monitors your weight, but if you want a full picture of your progress, you'll have to share data using one of its partner services. It syncs with about 50 of them, everything from apps that manage your medical records to a game that lets you earn life points. Runners love the linkup with RunKeeper, but I'm looking to keep tabs on other activities, so I grab Fitbit, a fancy pedometer that's my entry into the world of self-tracking.

Fitbit is so insanely simple it comes with no instructions, just a Web address. Plug the base station into your computer, create a profile, and Fitbit will do the rest.

Or get you to do it. Fitbit is about the size of your thumb. It's elegant but a little geeky – "your dork clip," my wife calls it. It tracks my steps, and along with logging the miles I've traveled and calories I've burned, Fitbit has an altimeter that uses barometric pressure to calculate the floors I've climbed and hills I've run. All this comes up on the LED readout, along with a flower graphic that grows when I'm active and shrinks when I'm sedentary. And if I wear it at night (there's a wristband), Fitbit will evaluate my sleep. ("You're wearing your dork clip to bed?" my wife asks, incredulously.)

The LED screen also flashes messages whenever I pick it up – encouragements like ready? and burn it and stepgeek, but also endearments like hold me and love ya. These create an almost instant feeling of tech eroticism – a combination of that sensation when you've unboxed a new gadget and can't put it down until you've figured it out and the flush of being with someone new when you can't keep your hands off each other. I keep pulling Fitbit – or Fitty, as I soon begin to think of her – off my belt and checking in. And what do you have to tell me, little one? How many steps have I taken? How many calories have I burned? Aw, that's sweet, Fitty – I think I will burn it. You're right, I am a step geek!

Yup. I'm in a relationship with a piece of plastic. And as in any new relationship during the infatuation phase, I'm desperate to please. Fitbit sets a goal of 10,000 steps, five miles, and 10 floors a day. Not wanting to disappoint on days when I can't get in a workout, I get off the subway a few stops early so I can get in more steps. I want to make those numbers, push past those minimums, so I spend lunchtime walking with no particular place to go for 45 minutes, just to impress Fitty by beating yesterday's number. One morning when I can't get to the gym, I run the stairs in my apartment building. After 33 floors my legs are burning. When I check in with the Fitbit website later, Fitty rewards me with this message: you have climbed: big ben.

I know, I know – stomach-churningly cute. But you just don't understand what Fitty and I have going. Though it won't last forever – it never does – at the start, I keep thinking of the Velvet Underground's love song "I'll Be Your Mirror" and its promise of blank devotion: "Reflect what you are, in case you don't know." Except I'm reflecting this back to myself (aren't I?), and what I am is changing. In the first week Fitty and I are together, I lose three and a half pounds and my BMI is 25.1. My goal is within reach.Some people build their lives around numbers. Bankers. Athletes. Nerds. These people thrive on competition, accomplishment, and measurement. I am not one of these people. I have never liked numbers. I like wine, women, and song. I built my life around those things, though over time, with less wine and one woman. Still, there is no running from the numbers.

In my teens, it was the SATs. In my twenties, my checkbook. In my thirties, my waistline. Forties, cholesterol. I have always conceived of my life with numbers as an ongoing war, one defined by the unshakable certainty that one day the numbers – which have no feelings, no allegiances, no vulnerabilities, nothing but their own certitude and progression – would win.

Fitbit makes the numbers into something fun. For one thing, the tables are turned: Instead of the numbers weighing me down, I'm moving them around. Applied effort yields quantifiable results.

If Fitbit is my digital girlfriend, the Fitbit log is my instructor in the language of numbers. I try out a lot of tracking sites and mobile apps during my numerical journey, but the Fitbit dashboard stands out as the most useful. I record my mood and sleep quality in the morning, my post-gym activities, and (thanks to the mobile app) anything I eat.

The food log is the game changer. I've studied up plenty on the nutritional basics in the past, but beyond understanding the essential difference between cheese fries and brown rice, I've never thought hard about calories. Yet soon I'm inputting the nutritional deets of my breakfast cereal into the Fitbit database and haunting websites where posters argue over the caloric content of black coffee. And once I'm in, I'm in. Measuring cups come out (turns out I'm eating a half cup of low-fat yogurt in the morning, not a cup – 85 calories saved!), I'm buying less food at lunch (580 calories in a large lentil soup? I'll have a medium), and I'm cooking at home more (which gives me portion control and detailed knowledge of ingredients).

Is this a pain in the ass? You bet. It makes eating feel like a math equation where I'm constantly checking the answer key in the back of the book. Does it work? Totally. Quickly. Scientifically. A 2008 Kaiser Permanente study says the more you log, the more you lose, and it's easy to see why. I'm conscious of everything that goes into my mouth. So naturally less goes in, and what does is more of the right stuff.

But it's more than that. The tech thing is a gas at first, like turning my body into a video game. The Fitbit dashboard has a handy pie chart of the calories you have left to eat in a given day – looks like Pac-Man! I also geek out on the bar graphs for calories burned and steps taken and the line graphs of weight and body fat.

And I like what I see. Two weeks after I start with Fitbit, I'm down six and a half pounds, and my BMI is 24.7. I've hit my goal, and it feels like I've barely started. So I upload a new goal (185) to the Fitbit dashboard. This takes just two more weeks, during which time I notice my body fat starting to dip. I'm adding lean mass. The numbers are good. Fitty is impressed. I want more.Infatuation has a way of wearing off. And once I start focusing on Fitty's flaws, it's a bit of a crush killer. At first, I loved how small and unobtrusive Fitbit was. Then I spend an afternoon looking for it under my desk (it had stuck to the lining of my coat), and when it slips off my belt one afternoon, I have to buy another. More important, it doesn't do well counting calories burned for some activities, such as biking, because I'm wearing it clipped to my waist and it reads me as stationary. I realize this the day I come in from a 40-mile bike ride to find Fitty has a message waiting for me: you have climbed: burj khalifa. That's the world's tallest tower, in Dubai. Awesome! Fitty has logged the hills I've biked up as 276 floors. But it has also calculated the distance at a mere 12.61 miles. The pain of the disappointment hurts more than the ache in my quads.

It's the same problem for spinning, though a fellow spin geek recommends a simple hack: Clip the Fitbit to the bottom of my shorts so it logs more movement. Only before I get a chance to try this, I drown my Fitbit in sweat during a hard spin class and it dies. (Yeah, I sweat a lot.) Following the Fitbit FAQ on rebooting your device after you run it through the laundry (a more common issue, apparently, than drenching it in perspiration), I leave it overnight in a bowl of uncooked rice. It flickers back to life but never works again. Big up to Fitbit customer service, which sends me a new one when I email them about this problem, but clearly I need an upgrade.

I get a Scosche MyTrek heart monitor, a watchlike device built for rigorous exercise, worn just below the elbow, which feeds data to your phone. Set it to your desired heart rate, and a voice prompt will come through your headphones and tell you when to step it up or slow it down.

In theory, this will produce numbers nirvana: a perfect workout with an accurate calorie count, but intuitive, it's not. Eight times in, I finally have MyTrek figured out – and a new level of hell opens up: The affectless female voice telling me to "go faster" can't be appeased for long, since I'm constantly slipping into or out of the fitness zone, the way an ordinary human running on a crowded city sidewalk will. One morning I pass through a cloud of plaster dust raised by construction workers gutting an apartment building only to find myself stuck behind a dude Occupying the Sidewalk to enjoy his 8:30 am joint. For an excruciating few minutes, I'm coughing, plodding along, and hearing a woman who just doesn't get me bark the same instructions: "Go faster."

Then I get home and find the pulse monitor hasn't worked for most of the run. It was a solid run, but without the numbers it doesn't seem to count, or even to have happened. You want to finish a workout with elevated spirits and an elevated heart rate, but the frustration is pretty overwhelming and surprisingly lasting.

This is the dark side of fitness tech: Draw your encouragement and validation from a device and you'll lose sight of the experience itself. Sometimes I feel like I'm trying to drive by watching the speedometer instead of the road.

In frustration, I recalibrate. Instead of just chasing numbers, I start chasing the buzz that comes with my increasing activity and my decreasing BMI. And the funny thing is, it works. Using my tech off and on, I meet my goal of 185, and then my weight drops below 180, and then below 175. My body fat continues to drop. Not much, but enough that I have muscle definition I'd never seen before. An actress friend visiting from L.A. pronounces me "chiseled and shit" and asks what I'm doing. I attend my 30th high school reunion weighing about four pounds more than I did in high school.

It's like the numbers are inside mie now. I've learned what they have to tell me and internalized them. It isn't about whether I'm thinking about them or tracking them. I'm living them.

And as they, and I, continue to shrink (I've lost three inches from my waistline and dropped a suit size), I can feel myself growing. Things that used to seem impossible are simple to me now – my goal had been four days a week of exercise. I'm fitting in five. And then six. One morning the weather is so good that, not wanting to miss out on a perfect day, I take the subway uptown at 7 o'clock, before work, and walk over to Carl Schurz Park, one of my favorite spots in Manhattan, an elevated patch of green way above the East River. I sit for a while watching the river flow, then run downtown all the way home, about 7.5 miles, and tweet the results (58:12 minutes, avg. pulse of 152, burned 724 calories) because I'm so happy the MyTrek pulse monitor worked.

I have no idea when I became this guy.Do I want to live my life strapped into a heart monitor, or logging the calories in every square of dark chocolate I eat? No. I like to think of myself as more than the sum total of the bodily functions that I can quantify. But I sure do like the results of the quantification.

Scientists talk about the observer effect, that the very act of observation changes what's being observed. There's something obvious and ancient about this – it's why God is pictured up in heaven, watching over us. Just the idea of someone watching does the trick. A 2010 study at Newcastle University found hanging posters of faces on the wall prompted people to clean up after themselves more.

But what if the eyes are your own? What if the observer and the observed are one and the same? At first, I thought of Fitbit as a new girlfriend – can't keep away at the start, give up stuff just to be together, and when it all burns out in six to eight weeks, Fitty keeps emailing me (something about "weekly progress reports"), even though I've lost interest. But when I go back to Fitbit with weight maintenance in mind, I begin to think of it differently: an exoskeleton superego, helping me ride herd on the impulses of my id.

Eat carefully, exercise regularly. Basic stuff. But I need help. So I carry Fitbit in my pocket everywhere, or clip it to my gym bag. It's a reminder. It emails me progress reports and Foursquare-like badges (you've climbed as high as a hot air balloon travels, and that's 2,000 floors!). But it's something more. Maybe it is my mirror after all. It only works if I watch it back.

I've always conceived of my life with numbers as a war, so say we've negotiated a demilitarized zone of mutual observation. Except this isn't really a fight anymore. It feels...different.

If I thought the numbers had the capacity for feeling, I'd say we've achieved mutual respect. For a long time, I paid them no attention. But it turns out that was giving them too much power. If I ignored them, they just got bigger, more intimidating. For a long time, I thought they had the path staked out. That it was just a matter of how fast I was going their way. But I might be able to use them to chart my own course. With the help of some tech to navigate.

My scale is still talking to me. Only now, I'm talking back.

Calorie Counting
"How are you going to log that?" a friend asks as I bite into a bluefish sandwich. Easy: bluefish, 186 calories; spicy mayo, 110; Portuguese bun, 200. Total: 496. Two websites consulted, 58.7 seconds elapsed, plus another 45 seconds to add a custom food to my Fitbit log with an app (and I added 100 calories because when you're at a restaurant, you're guessing at portion and preparation – and I'm guessing that bun was buttered). Calorie counting is a nuisance, but it's not that hard anymore. Fitbit and other monitors like BodyMedia have libraries with thousands of entries you can rely on; websites like MyFitnessPal and SparkPeople have tons of info as well. And chain restaurants have info online. The logging habit can be difficult to acquire, but when you're burning more than you're eating, the feeling of triumph makes it easy to stick with. And the corresponding feelings of shame when you're not mean you'll work that much harder.

A Case For Going to Class
My first spinning class was over two years ago, and since then, I've become more than just a group-fitness convert – I'm the dipshit in the front row whoo-ing at the instructor when he asks how everyone is feeling. That's because I'm feeling excellent, and thanks for asking. Studies suggest group activities release feel-good chemicals in the brain, and that group fitness fuels a sense of shared goals. And there's even a series of Canadian studies that tells me what I know from experience: A group class means you'll show up, be on time, and actually get a workout in. It costs more than joining a gym, but unless you're among the virtuous few who actually use their gym memberships, it's a cheaper way into appointment fitness than a personal trainer. I used concierge fitness site Fitist to try out boxing and cross-training classes, as well as yoga and spinning. And I stuck with them. Now I'm 18 pounds lighter and have ­better definition than ever. Whoo!