Many of us use the pedometer integrated into your mobile phone to monitor the number of steps taken during the day and use this data to evaluate your level of sedentary lifestyle. But how does the smartphone understand how many steps we take? And most importantly, is the count 100% accurate? In short, the smartphone uses sensors, such asaccelerometer and the gyroscope, to determine what movements the device performed and “translate” them into a measurement of the steps taken. The measurement, however, is not always perfect and, according to some recent studies, in a day it can count hundreds of “ghost” steps.
What sensors does your smartphone use to count steps
Virtually all smartphones on the market integrate sensors used to count steps. Among these is theaccelerometer. What is it about exactly? Of a small device which, as its name suggests, has the task of measure the acceleration variations that occur on the X, Y and Z axes relating to the device in which it is integrated (in this case the smartphone). Reading the acceleration variationsthe accelerometer is able to determine whether you are moving in space or not and also in which direction and this allows you not only to rotate what is visible on the screen when you turn the device, but also allows you to count the steps taken with the smartphone.
There are various types of accelerometers used in different fields and for different purposes. As for smartphones, they are usually used capacitive accelerometersequipped with sensors MEMS (Micro Electro-Mechanical System or “Micro Electro-Mechanical Systems”), which collect the acceleration variations given by the movements undergone by the smartphone and which are then sent to the motion processor. The latter then processes the data collected by the accelerometer and correlates them with the information coming from the other motion sensors, so as to determine whether the user intends to rotate the device screen, whether he has taken a step and so on. .
In this process, even the gyroscope has an important role. This is another motion sensor that goes to measure angular velocity (therefore the rotation). This particular feature allows the processor to correctly understand (in the vast majority of cases) the difference between taking a step or simply lifting the phone from the desk, for example.
In practice, therefore, thanks to these sensors the smartphone obtains its orientation in space and speed variations repeatedly over time: from the analysis of this data, under appropriate conditions, the mobile phone is able to “decide” whether these variations are due to steps and, in this case, increase the count.
If the GPS of your smartphone is active, the latter is also involved in measuring steps thanks to the data tracking the distances traveled which, combined with the information coming from the accelerometer and gyroscope (and the data provided by the user during the configuration phase of the pedometer apps, such as height, gender, weight and stride length) allow not only to have more accurate statistics on the steps taken, but also to determine the number of calories burned, the total distance traveled and so on.
How accurate is step counting with your smartphone
A study published in 2022 tried to verify How accurate is step counting with your cell phone. The study in question compared data from a accelerometer for medical use (ActiGraph-GT3X) with those recorded by a pedometer app (WeRun). Both solutions were used on a sample of 103 people who used them for three step counting sessions lasting a week each (for a total of 21 days of measurement). The data collected demonstrated that the smartphone app overestimated the average number of daily steps by nearly 500.
The study, therefore, confirmed what many of us have experienced empirically by using the smartphone as a pedometer: it is possible to use it to have a plausible estimate of the steps taken during the day, but it is not possible to expect a level of error close to zero from solutions of this type. To minimize cell phone errors in counting steps, however, we advise you to place it in your pocket instead of keeping it in your backpack or bag given that, in the latter case, it would be more difficult to trace the forward movements made with its limbs.
