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     Lean app

Get ready (sec)            
Baseline (sec)
Vibration (ms)
Warning angle (°)
Grace period (ms)
Report period (sec)  


Time (ms), Alarms, Observations, Average lean (°) in period, Alarms, Observations, Average lean (°) cumulative,


This app causes a smartphone to vibrate when tilted. If worn on the body, it can be used to monitor posture.

Default use

  1. Press the start button.
  2. You feel the smartphone vibrate briefly.
  3. You now have 20 seconds to get ready for the baseline:
    • with the phone fixed securely to the body;
    • with you sitting or standing with a good posture.
  4. The phone vibrates again.
  5. Stay with a good posture for 10 seconds to get a baseline.
  6. Vibrate again.
  7. The system is running.
  8. The phone will vibrate if the lean continuously exceeds its limit of 10 degrees for more than 5 seconds.

Other uses

By increasing the angle and the grace period you can stop the vibrations occuring. In this case the app will continue to report the lean angle. Thus, becoming a pure measuring device. Additionally, it is possible, but untested, that the app may impact on falls and sleep attacks.


Duration to prepare (sec). Default 20 sec. The time to get ready for the baseline.

Duration of baselining (sec). Default 10 sec. The time to sit or stand with a good posture. The program averages the accelerometer readings. This approximates to local vertical.

Duration of vibration (ms). Default 300ms, i.e. 0.3 sec.

Warning angle (degrees). Default 10°. When the angle between the baseline vertical and the present vertical exceeds this value for a long enough period of time the vibration will be fired.

Grace period. Duration of continuous fails required to raise vibration (ms). Default 5000, i.e. 5 sec. This is the important part of the algorithm. It removes many false positives. For instance, looking down briefly should not trigger the vibrations. This also filters out most accelerations due to movement.

Duration of group (sec). Default 60 sec. Statistics of the lean are written to the screen. every 1 minute.


For the app to work your smartphone needs to have an accelerometer. The easiest way to check if this is the case is to try to run the app and see if it works: if there's no output, there's no accelerometer.

You need to be on-line to use this app.

The app has only been tested on Android smartphones.

Avoid the smartphone going into sleep mode

For the app to work it is necessary to overcome two competing problems:

Smartphones go into sleep mode if they are not being used. This can occurs after as little as 15 seconds. If this happens, the app does not work. There are two options available:

You can extend the time before your smartphone goes into sleep mode. You can do this by going into Settings, Display, Sleep. Unfortunately, a typical upper value is 30 minutes, which is too short for most work.

Alternatively, you can download a free app, like Keep Screen On!, which does what its name says.

Positioning on the body

The phone needs to be securely attached to a part of your body that best represents your posture. For many people this will be their head. A simple, rough and ready solution is to velcro the phone to the underside of a tight fitting ski hat.

Effect on posture

Identifying poor posture does not in itself lead to better posture. Users are encouraged to seek medical advice on what is the best posture for them.

Release history

19th October 2017. John Turner. Initial release.