A little backstory for this. I developed an app that plays a sword unsheathing sound whenever the person takes his phone out of the pocket. I searched the web for a way to detect whether or not the device is in a pocket, but didn’t find any explicit implementation. So here we are.

The link to the project: https://github.com/IvanLudvig/SwordSoundApp

How to detect if the device is in a pocket

The main signs that the phone is in a pocket are: little light, vertical upside-down position and lack of space. These parameters can be obtained by the Light sensor, Accelerometer and Proximity sensor.

Implementation

Here’s how I get the needed values from the device’s sensors (in SensorListener.java):

    @Override
    public void onSensorChanged(SensorEvent event) {

        if (event.sensor.getType()==Sensor.TYPE_ACCELEROMETER) {
            g = new float[3];
            g = event.values.clone();

            double norm_Of_g = Math.sqrt(g[0] * g[0] + g[1] * g[1] + g[2] * g[2]);

            g[0] = (float) (g[0] / norm_Of_g);
            g[1] = (float) (g[1] / norm_Of_g);
            g[2] = (float) (g[2] / norm_Of_g);

            inclination = (int) Math.round(Math.toDegrees(Math.acos(g[2])));
            accReading.setText("XYZ: "+round(g[0])+",  "+round(g[1])+",  "+round(g[2])+"  inc: "+inclination);
        }
        if(event.sensor.getType()==Sensor.TYPE_PROXIMITY){
            proximityReading.setText("Proximity Sensor Reading:" + String.valueOf(event.values[0]));
            rp=event.values[0];
        }
        if(event.sensor.getType() == Sensor.TYPE_LIGHT){
            lightReading.setText("LIGHT: " + event.values[0]);
            rl=event.values[0];
        }
        if((rp!=-1) && (rl!=-1) && (inclination!=-1)){
            main.detect(rp, rl, g, inclination);
        }

}

As you can see, the method detect is called, which is located in MainActivity.java. This is the core of the mechanism. It compares to current values (obtained by sensors) to such values that indicate that the phone is in a pocket. The border values given by me are pure approximation. So keep in mind, they have to be adjusted in order to achive accurate results.

public void detect(float prox, float light, float g[], int inc){
        if((prox<1)&&(light<2)&&(g[1]<-0.6)&&( (inc>75)||(inc<100))){
            pocket=1;
            //IN POCKET
        }
        if((prox>=1)&&(light>=2)&&(g[1]>=-0.7)){
            if(pocket==1){
                playSound();
                pocket=0;
            }
            //OUT OF POCKET
        }
}

In my example the border values are 1 for proximity sensor, 2 for light sensor and -0.6/-0.7 for accelerometer (it also takes account of inclination).

P.S: This mechanism isn’t really precise.

Thanks for reading. I can answer any questions if there are any. Good luck developing. More to come!