I was at an Italian restaurant in Melbourne, listening as a woman named Lesley talked about her housekeeper, an immigrant to Australia who earlier that day had cleaned the bathroom countertops with a bottle of very expensive acne medication: "She's afraid of the vacuum cleaner and can't read or write a word of English, but other than that she's marvellous."

Lesley works for a company that goes into developing countries and trains doctors to remove cataracts. "It's incredibly rewarding," she said as our antipasto plate arrived. "These are people who've been blind for years, and suddenly, miraculously, they can see again." She brought up a man who'd been operated on in a remote area of China. "They took off the bandages, and for the first time in two decades he saw his wife. Then he opened his mouth and said, 'You're so... old'. "

Lesley pushed back her shirtsleeve, and as she reached for an olive I noticed a rubber bracelet on her left wrist. "Is that a watch?" I asked.

"No," she told me. "It's a Fitbit. You sync it with your computer, and it tracks your physical activity." I leaned closer, and as she tapped the thickest part of it a number of glowing dots rose to the surface and danced back and forth. "It's like a pedometer," she continued. "But updated, and better. The goal is to take 10,000 steps per day, and, once you do, it vibrates."

I forked some salami into my mouth. "Hard?"

"No," she said. "It's just a tingle."

The FitBit: “It’s like a pedometer, but updated, and better.”

A few weeks later, I bought a Fitbit of my own, and discovered what she was talking about. Ten thousand steps, I learned, amounts to a little more than four miles for someone my size – 5ft 5in. It sounds like a lot, but you can cover that distance in the course of an average day without even trying, especially if you have stairs in your house, and a steady flow of people who regularly knock, wanting you to accept a package or give them directions or just listen patiently as they talk about birds, which happens from time to time when I'm at home in West Sussex. One April afternoon, the person at my door hoped to sell me a wooden bench. It was bought, he said, for a client whose garden he was designing. "Last week she loved it, but now she's decided to go with something else." In the bright sunlight, the fellow's hair was as orange as a Popsicle. "The company I ordered it from has a no-return policy, so I'm wondering if maybe you'd like to buy it." He gestured toward an unmarked van idling in front of the house, and seemed angry when I told him that I wasn't interested. "You could at least take a look before making up your mind," he said.

I closed the door a few inches. "That's OK." Then, because it's an excuse that works for just about everything, I added: "I'm American."

"Meaning?" he asked.

"We... stand up a lot," I told him.

"Oldest trick in the book," my neighbour Thelma said when I told her what had happened. "That bench was stolen from someone's garden, I guarantee it."

This was seconded by the fellow who came to empty our septic tank. "Pikeys," he said.

"Come again?"

"Tinkers," he said. "Pikeys."

"That means Gypsies," Thelma explained, adding that the politically correct word is "travellers".

I was travelling myself when I got my Fitbit, and because the tingle feels so good, not just as a sensation but also as a mark of accomplishment, I began pacing the airport rather than doing what I normally do, which is sit in the waiting area, wondering which of the many people around me will die first, and of what. I also started taking the stairs instead of the escalator, and avoiding the moving pavement.

"Every little bit helps," my old friend Dawn, who frequently eats lunch while hula-hooping and has been known to visit her local Y three times a day, said. She had a Fitbit as well, and swore by it. Others I met weren't quite so taken. These were people who had worn one until the battery died. Then, rather than recharging it, which couldn't be simpler, they'd stuck it in a drawer, most likely with all the other devices they'd lost interest in over the years. To people like Dawn and me, people who are obsessive to begin with, the Fitbit is a digital trainer, perpetually egging us on. During the first few weeks that I had it, I'd return to my hotel at the end of the day, and when I discovered that I'd taken a total of, say, 12,000 steps, I'd go out for another 3,000.

"But why?" my boyfriend Hugh asked when I told him about it. "Why isn't 12,000 enough?"

"Because," I told him, "my Fitbit thinks I can do better."

I look back at that time and laugh – 15,000 steps – Ha! That's only about seven miles! Not bad if you're on a business trip or you're just getting used to a new prosthetic leg. In Sussex, though, it's nothing. Our house is situated on the edge of a rolling downland, a perfect position if you like what the English call "rambling". I'll follow a trail every now and then, but as a rule I prefer roads, partly because it's harder to get lost on a road, but mainly because I'm afraid of snakes. The only venomous ones in England are adders, and even though they're hardly ubiquitous, I've seen three that had been run over by cars. Then I met a woman named Janine who was bitten and had to spend a week in the hospital. "It was completely my own fault," she said. "I shouldn't have been wearing sandals."

"It didn't have to strike you," I reminded her. "It could have just slid away."

Janine was the type who'd likely blame herself for getting mugged. "It's what I get for having anything worth taking!" she'd probably say. At first, I found her attitude fascinating. Then I got vindictive on her behalf, and started carrying a snake killer, or, at least, something that could be used to grab one by the neck and fling it into the path of an oncoming car. It's a hand-size claw on a pole, and was originally designed for picking up litter. With it I can walk, fear snakes a little less, and satisfy my insane need for order all at the same time. I've been cleaning the roads in my area of Sussex for three years now, but before the Fitbit I did it primarily on my bike, and with my bare hands. That was fairly effective, but I wound up missing a lot. On foot, nothing escapes my attention: a crisp bag stuffed into the hollow of a tree, an elderly mitten caught in the embrace of a blackberry bush, a mud-coated matchbook at the bottom of a ditch. Then, there's all the obvious stuff: the cans and bottles and great greasy sheets of paper that fish and chips comes wrapped in. You can tell where my territory ends and the rest of England begins. It's like going from the rose arbor in Sissinghurst to Fukushima after the tsunami. The difference is staggering.

Since getting my Fitbit, I've seen all kinds of things I wouldn't normally have come across. Once, it was a toffee-coloured cow with two feet sticking out of her. I was rambling that afternoon, with my friend Maja, and as she ran to inform the farmer I marched in place, envious of the extra steps she was getting in. Given all the time I've spent in the country, you'd think I might have seen a calf being born, but this was a first for me. The biggest surprise was how unfazed the expectant mother was. For a while, she lay flat on the grass, panting. Then she got up and began grazing, still with those feet sticking out.

"Really?" I said to her. "You can't go five minutes without eating?"

Around her were other cows, all of whom seemed blind to her condition.

"Do you think she knows there's a baby at the end of this?" I asked Maja after she'd returned. "A woman is told what's going to happen in the delivery room, but how does an animal interpret this pain?"

I thought of the first time I had a kidney stone. That was in New York, in 1991, back when I had no money or health insurance. All I knew was that I was hurting, and couldn't afford to do anything about it. The night was spent moaning. Then I peed blood, followed by what looked like a piece of gravel from an aquarium. That's when I put it all together.

What might I have thought if, after seven hours of unrelenting agony, a creature the size of a full-grown cougar emerged, inch by inch, from the hole at the end of my penis and started hassling me for food? Was that what the cow was going through? Did she think she was dying, or had instinct somehow prepared her for this?

Maja and I watched for an hour. Then the sun started to set, and we trekked on, disappointed. I left for London the next day, and when I returned several weeks later, and hiked back to the field, I saw mother and child standing side by side, not in the loving way that I had imagined but more like strangers waiting for the post office to open.

Back then I was averaging 25,000 steps, or around 10.5 miles per day. Trousers that had grown too snug were suddenly loose again, and I noticed that my face was looking a lot thinner. Then I upped it to 30,000 steps, and started moving farther afield.

"We saw David in Arundel picking up a dead squirrel with his grabbers," the neighbours told Hugh. "We saw him outside Steyning rolling a tire down the side of the road"; "...in Pulborough dislodging a pair of Y-fronts from a tree branch".

Before the Fitbit, once we'd eaten dinner I was in for the evening. Now, though, as soon as I'm finished with the dishes I walk to the pub and back, a distance of 3,895 steps. There are no street lights where we live, and the houses I pass at 11pm are either dark or very dimly lit. I often hear owls, and the flapping of woodcocks disturbed by the beam of my flashlight. One night, I heard a creaking sound, and noticed that the minivan parked a dozen or so steps ahead of me was rocking back and forth. A lot of people where we live seem to have sex in their cars. I know this because I find their used condoms, sometimes on the road but more often just off it, in little pull-over areas. In addition to spent condoms, in one of the spots that I patrol I regularly pick up empty KFC containers and a great number of soiled Handi Wipes. Do they eat fried chicken and then have sex, or is it the other way round? I wonder.

I look back on the days I averaged only 30,000 steps and think, honestly, how lazy can you get? When I hit 35,000 steps a day, Fitbit sent me an e-badge, and then one for 40,000, and 45,000. Now I'm up to 60,000, which is 25.5 miles. Walking that distance at the age of 57, with completely flat feet while lugging a heavy bag of garbage, takes close to nine hours – a big block of time, but hardly wasted. I listen to audiobooks, and podcasts. I talk to people. I learn things: the fact, for example, that, in the days of yore, peppercorns were sold individually and, because they were so valuable, to guard against theft the people who packed them had to have their pockets sewed shut.

At the end of my first 60,000-step day, I staggered home with my flashlight knowing that I'd advance to 65,000, and that there will be no end to it until my feet snap off at the ankles. Then it'll just be my jagged bones stabbing into the soft ground. Why is it some people can manage a thing like a Fitbit, while others go off the rails and allow it to rule, and perhaps even ruin, their lives? While marching along the roadside, I often think of a TV show that I watched a few years back – Obsessed, it was called. One of the episodes was devoted to a woman who owned two treadmills and walked like a hamster on a wheel from the moment she got up until she went to bed. Her family would eat dinner, and she'd observe them from her vantage point beside the table, panting as she asked her children about their day. I knew that I was supposed to scoff at this woman, to be, at the very least, entertainingly disgusted, but instead I saw something of myself in her. Of course, she did her walking on a treadmill, where it served no greater purpose. So it's not like we're really that much alike. Is it?

In recognition of all the rubbish I've collected since getting my Fitbit, my local council is naming a garbage truck after me. The fellow in charge emailed to ask which font I would like my name written in, and I answered 'Roman'. "Get it?" I said to Hugh. "Roamin'." He lost patience with me somewhere around the 35,000 mark, and responded with a heavy sigh.

Shortly after I decided on a typeface, for reasons I cannot determine, my Fitbit died. I was devastated when I tapped the broadest part of it and the little dots failed to appear. Then I felt a great sense of freedom. It seemed that my life was now my own again. But was it? Walking 25 miles, or even running up the stairs and back, suddenly seemed pointless, since, without the steps being counted and registered, what use were they? I lasted five hours before I ordered a replacement, express delivery. It arrived the following afternoon, and my hands shook as I tore open the box. Ten minutes later, my new master strapped securely around my left wrist, I was out the door, racing, practically running, to make up for lost time. µ

A version of this article first appeared in 'The New Yorker'