# How do the pulse monitor and pedometer on my Fitbit bracelet thingie work? **URL:** \ **Category:** Factual Questions\ **Created:** [March 8, 2015, 7:19pm UTC](https://boards.straightdope.com/t/how-do-the-pulse-monitor-and-pedometer-on-my-fitbit-bracelet-thingie-work/714546 "2015-03-08T19:19:43Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [March 8, 2015, 7:19pm UTC](https://boards.straightdope.com/t/how-do-the-pulse-monitor-and-pedometer-on-my-fitbit-bracelet-thingie-work/714546/1 "2015-03-08T19:19:43Z")
See subject. It occurred to me I never knew how _any_ pedometer works. My guesses, each of which I think is too complicated by half: Heart rate monitor: Strain-guage for pressure sensation from vein; or CMOS that notes the occlusion of the little LEDs on the vein side, occurring each time the normal-“cylinder” (cross section) of the vein splats out on each pulse. Pedometer: Accelerometer, adjusted for sudden spike to ignore more-continuous hand motions. ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [March 8, 2015, 7:52pm UTC](https://boards.straightdope.com/t/how-do-the-pulse-monitor-and-pedometer-on-my-fitbit-bracelet-thingie-work/714546/2 "2015-03-08T19:52:51Z")
> [@Leo\_Bloom](#): > > See subject. > > It occurred to me I never knew how _any_ pedometer works. > > My guesses, each of which I think is too complicated by half: > > Heart rate monitor: > Strain-guage for pressure sensation from vein; or > CMOS that notes the occlusion of the little LEDs on the vein side, occurring each time the normal-“cylinder” (cross section) of the vein splats out on each pulse. > > Pedometer: > Accelerometer, adjusted for sudden spike to ignore more-continuous hand motions. You’ve got the Pedometer correct I think. The heart rate monitor registers the change in skin “color” from your pulse, sending light from a couple of leds and registering the level of returned light. (Off the top of my head.) ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [March 8, 2015, 8:19pm UTC](https://boards.straightdope.com/t/how-do-the-pulse-monitor-and-pedometer-on-my-fitbit-bracelet-thingie-work/714546/3 "2015-03-08T20:19:13Z")
Accelerator without gyros must be a strain-gauge also, right? ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [March 8, 2015, 9:06pm UTC](https://boards.straightdope.com/t/how-do-the-pulse-monitor-and-pedometer-on-my-fitbit-bracelet-thingie-work/714546/4 "2015-03-08T21:06:48Z")
> [@Leo\_Bloom](#): > > Accelerator without gyros must be a strain-gauge also, right? Yes, micro-machined 3-axis strain gauges. ---
**Author:** ![jharvey963](https://avatars.discourse-cdn.com/v4/letter/j/54ee81/32.png) [@jharvey963](https://boards.straightdope.com/u/jharvey963)\ **Post date:** [March 9, 2015, 3:41pm UTC](https://boards.straightdope.com/t/how-do-the-pulse-monitor-and-pedometer-on-my-fitbit-bracelet-thingie-work/714546/5 "2015-03-09T15:41:20Z")
Something that bothers me about the FitBit and all other devices of this type: Do they distinguish between walking and, say, riding in a car? And if so, _how_? J. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [March 9, 2015, 5:17pm UTC](https://boards.straightdope.com/t/how-do-the-pulse-monitor-and-pedometer-on-my-fitbit-bracelet-thingie-work/714546/6 "2015-03-09T17:17:47Z")
> [@jharvey963](#): > > Something that bothers me about the FitBit and all other devices of this type: Do they distinguish between walking and, say, riding in a car? And if so, _how_? > > J. I would suspect that they look at the acceleration signal. Walking would generate a repetitive up/down signal, while driving in a car would be much smoother (and probably more acceleration, too). ---
**Author:** ![zombywoof](https://avatars.discourse-cdn.com/v4/letter/z/9e8a1a/32.png) [@zombywoof](https://boards.straightdope.com/u/zombywoof)\ **Post date:** [March 9, 2015, 5:50pm UTC](https://boards.straightdope.com/t/how-do-the-pulse-monitor-and-pedometer-on-my-fitbit-bracelet-thingie-work/714546/7 "2015-03-09T17:50:53Z")
> [@jharvey963](#): > > Something that bothers me about the FitBit and all other devices of this type: Do they distinguish between walking and, say, riding in a car? My Fitbit worked very well at not counting any false “steps” while driving/riding in a car (on normal paved roads) before I lost it. ---
**Author:** ![gazpacho](https://avatars.discourse-cdn.com/v4/letter/g/6f9a4e/32.png) [@gazpacho](https://boards.straightdope.com/u/gazpacho)\ **Post date:** [March 9, 2015, 6:08pm UTC](https://boards.straightdope.com/t/how-do-the-pulse-monitor-and-pedometer-on-my-fitbit-bracelet-thingie-work/714546/8 "2015-03-09T18:08:45Z")
> [@jharvey963](#): > > Something that bothers me about the FitBit and all other devices of this type: Do they distinguish between walking and, say, riding in a car? And if so, _how_? > > J. My fitbit for the most part does a pretty good job with not counting car bumps as steps. There was one trip I did in Glacier National Park on the old red buses they have. I was sitting in the back and it seemed to me that fit bit was giving me steps because of the rough ride. ---
**Author:** ![kferr](https://avatars.discourse-cdn.com/v4/letter/k/71e660/32.png) [@kferr](https://boards.straightdope.com/u/kferr)\ **Post date:** [March 10, 2015, 12:05pm UTC](https://boards.straightdope.com/t/how-do-the-pulse-monitor-and-pedometer-on-my-fitbit-bracelet-thingie-work/714546/9 "2015-03-10T12:05:55Z")
It does seem very good at distinguishing steps from activities that are moving but smooth. If I ride my road bike it barely registers anything, but off road on the mountain bike it will register some phantom steps. ---
**Author:** ![Hypno-Toad](https://avatars.discourse-cdn.com/v4/letter/h/b2d939/32.png) [@Hypno-Toad](https://boards.straightdope.com/u/Hypno-Toad)\ **Post date:** [March 10, 2015, 2:32pm UTC](https://boards.straightdope.com/t/how-do-the-pulse-monitor-and-pedometer-on-my-fitbit-bracelet-thingie-work/714546/10 "2015-03-10T14:32:41Z")
> [@kferr](#): > > It does seem very good at distinguishing steps from activities that are moving but smooth. If I ride my road bike it barely registers anything, but off road on the mountain bike it will register some phantom steps. When I hit certain rumbly sections of pavement on my bike, it puts my fitbit into sleep mode. Sort of annoying. Also annoying is that a hard, sweaty bike ride into a headwind seems to count for less to my fitbit than a casual walk. ---
**Author:** ![Mama\_Zappa](https://avatars.discourse-cdn.com/v4/letter/m/71e660/32.png) [@Mama\_Zappa](https://boards.straightdope.com/u/Mama_Zappa)\ **Post date:** [March 13, 2015, 3:29am UTC](https://boards.straightdope.com/t/how-do-the-pulse-monitor-and-pedometer-on-my-fitbit-bracelet-thingie-work/714546/11 "2015-03-13T03:29:32Z")
It can also get false negatives - I use a wristband version (versus a clip-on) and when I grocery shop, I’ve learned to put it in my pocket. Otherwise I spend 40 minutes in the store, and find I’ve walked a grand total of 300 steps (because of the hand being on the grocery cart handle).