NaiveStillDetection.mm

// The following is executed every 0.5s
        
CMAcceleration accel = data.acceleration;
double mag = sqrt(pow(accel.x, 2)+pow(accel.y,2)+pow(accel.z,2));

// The thresholds here are derived from manually experimenting. magnitude is in Gs. 1.0G is expected due to gravity

if (mag < 0.9275 || mag > 1.0903) {
    [self incrementActiveCount];
            
} else {
    [self incrementStillCount];
            
}

// The counts are necessary to reduce false positives. PHONE_STILL_COUNT is set to 120. PHONE_ACTIVE_COUNT is set to 5

- (void)incrementStillCount
{
    _stillCount++;
    if (_stillCount >= PHONE_STILL_COUNT) {
        // changes phone state to still. aka turns location services on
        [_stateDelegate phoneIsStill];
        _stillCount = 0;
        _activeCount = 0;
    }
   
}

- (void)incrementActiveCount
{
    _activeCount++;
    if (_activeCount >= PHONE_ACTIVE_COUNT) {
        //changes phone state to "normal". aka turns location services off
        [_stateDelegate phoneMoved];
        _activeCount = 0;
        _stillCount = 0;
    }
    
}