My husband considered it the perfect gift for an aging exercise enthusiast, a computerized wristwatch that counts my movements, nags and encourages me in equal measure, and even tracks my sleep. A close friend cautioned that the device only feeds my obsessive nature.

Both men are right. The Fitbit, which I received for my birthday July 4, is pushing me to reboot my already disciplined daily exercise habit. But when is enough, enough? The day I log 15,495 steps, I am exhausted by 8:30 p.m.

My Fitbit, meanwhile, urges me on (“Today is the day!”) and fuels my competitive spirit. The first time I pushed past my 10,000-steps goal for seven days straight, it exhorted me: “You crushed it!” I even earned a Helicopter Badge for climbing 500 floors.

Four weeks into owning a Fitbit, I already consider it an essential part  of my routine. It guilts me when I leave it on the kitchen counter so I can fix supper after work. “Hello, Amy,” it flashes when I strap it back on, in a tone that sounds eerily like my mother when I stayed out too late as a teenage girl.

On July 19, a sad day when my boss died suddenly of a heart attack, the watch greeted me with a simple, “Hi, friend.” It has come to know me and anticipate my needs.

Advice from the pros

Fitbit Flex, the first version of the tracker to be worn on a wrist rather than clipped on a waistband, was released in May 2013, four years after the San Francisco-based company (founded as Healthy Metrics Research) launched its Fitbit Classic Clip. Clearly I am late to the party.  But my device is new to me, and I’m extolling its virtues with all the zeal of the recently converted.

Peers over 60 use the Fitbit to track various health metrics such as weight, water consumption and sleep — which I perpetually shortchange — at an age when we no longer can take good health for granted.

• “I’m conscious of my resting BPM and actually get concerned when it’s elevated,” says my childhood friend Janey, 61, a doctor’s daughter who has always been knowledgeable about her health.
• “I wore out my first one so am on a newer version now,” says Diane, who is fit and trim at 61. “It has literally changed my exercise habits.”
• Helene, 66, began wearing a Fitbit two years ago because her employer incentivized it. She now walks longer distances in the morning and over lunch, and she expects those habits to continue once she retires this fall.

Like Helene, I used to track steps with a pedometer app on my iPhone. Despite walking to work and moving around throughout the day, I sometimes had trouble making 10,000 steps (an arbitrary measure of daily fitness that originated with a Japanese pedometer company in the 1960s). No longer.

Now I consciously stride the hallways at work, and up and down the stairs at home, because I know I’m getting credit for the effort. “Fitbit accounts for all the steps in a day, not just when I’m exercise-walking,” Helene notes.

Metrics and measurement

Even productive habits can start to own us.

My friend Diane engages in Fitbit exercise challenges with her family, but she refuses to wear the device to bed. Janey likes the various Fitbit community groups — my own app suggests Vegetarian, Yoga and Cycling (how does it know?) — but she removes her Fitbit sometimes “just to see if I can have it off for a day.”

I have run and walked 15,130 steps today, for a total of 7.16 miles. I’ve burned 1,983 calories. What do I miss when I measure every movement, every moment?

As a calendar-driven person whose work already ties me to my iPhone, I want to lose track of time, to let myself just be — at an age when I have earned that freedom. Should I reframe the phrase “off the clock” to “off the Fitbit”?

“LOL,” says Janey. “It usually doesn’t work.”