Pedometer Mechanisms - What Makes Your Pedometer Tick?

Pedometers and Fitness Trackers
Pedometers and Fitness Trackers. Wendy Bumgardner ©

Pedometers are quite different under the hood. The mechanisms used to count steps vary in ways that affect noise, accuracy, and longevity of the pedometer.

Accelerometers - Piezo-electric Pedometers - The Quiet Ones

Fitness trackers and fitness bands such as Fitbit use accelerometers that are silent and have no moving parts, so there is no annoying click with each step. Accelerometers may be dual-axis or tri-axis so they can work when tilted or in various positions.

Models can be designed to be worn as a wristband fitness tracker or carried as a pocket pedometer. For best accuracy, look for ones that claim to be tri-axis.

Tests show that accelerometers are more accurate than the old spring-lever mechanisms, especially when walking at slower speeds. The accelerometer uses a strain gauge, which measures how fast you are moving (inertia). This uses more battery juice, so users need to replace the batteries more often than with some other pedometers - every 6 months or so. Many fitness trackers have advanced features such as Bluetooth connectivity and lighted displays and require recharging daily or weekly.

Designers use algorithms to screen out motions that should not count as steps. This is especially important for wristband models.
Advantages

  • Silent
  • Can be designed to be worn as a wristband or clip to be worn or carried anywhere on the body.
  • More accurate than spring-lever pedometers for those with protruding waists, or if worn at various angles.

Disadvantages

  • Must replace battery more often, and fitness trackers with advanced features may require charging daily to weekly.

    Models

    Accelerometer Chips in Mobile Phones

    Mobile phones and other mobile devices use accelerometer chips to orient their screens. But beyond this function, they can count steps and detect speed and direction of motion. Apps can use that data display step counts and activity.

    Advantages

    • Silent and already built into the device.
    • Variety of apps available so you can choose the one you like best for any device.
    • More: Pedometer Apps

    Disadvantages

    • Need to replace your mobile device in order to get a better chip.

    Spring-Levered Pedometers with Coiled Spring

    A spring-levered pedometer mechanism moves with each step, the lever arm swinging downward and closing a contact to count a step, then the spring returning it to its original position. A coiled spring has a much longer lifespan and retains its accuracy more than a hairspring. Researchers have used the Yamax Digiwalker with the coiled spring mechanism as a gold-standard for accuracy.
    Advantages

    • Accurate
    • Longer battery life

      Disadvantages

      • Clicks
      • Not as accurate as the piezoelectric pedometers when tilted. Those with rounded stomachs may not get as accurate of a reading.

      Models

      Spring-Levered Pedometers with a Hairspring

      A hairspring will lose its accuracy much faster than a coiled spring. After about a million steps, the spring is weakened and it begins overcounting steps. A coiled spring retains its accuracy for over ten times longer. Most of the pedometers on the market use a hairspring rather than a coiled spring.

      What Makes a Pedometer Click so Loud?

      The clicking noise in a spring-levered pedometer comes from the closing of the contacts.
      Magnetic Switch: Some pedometers use a magnetic switch to close the contact - it clicks, but there is no actual contact being made.
      Metal Contacts: For those pedometers in which metal contacts metal, a pedometer can be made quieter by covering the contacts in rubber - which also lengthens the lifespan of the contacts. The Yamax Digiwalker models coat their contacts in rubber, making them quieter than most. Cheaper pedometers don't bother. A noisier metal contact pedometer is likely to have a shorter lifespan than a quieter pedometer.

      How Long Will the Pedometer Last?

      A Montana State University study by Dan Heil found that the hairspring pedometers would probably be accurate for only 18 months of use, under 1 million steps. The coiled spring mechanism in the Yamax Digiwalker was still going strong and accurate for many millions of steps, with an estimated lifespan of 4.5 years. Be sure to keep the battery-replacement instructions handy, or bookmark the company's web site for instructions.

      References
      "Spring-Levered versus Piezo-Electric Pedometer Accuracy in Overweight and Obese Adults," Crouter, Schneider, and Bassett, Medicine & Science in Sports & Exercise. 37(10):1673-1679, October 2005.
      "Validity of 10 Electronic Pedometers for Measuring Steps, Distance, and Energy Cost" Crouter, Schneider, Karabulut and Bassett. Medicine and Science in Sports and Exercise, 35 (10), 1779–1784.
      Montana State University Pedometer Longevity Study

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