Detect hard taps anywhere on iPhone through accelerometer

Question

I am trying to detect the taps which could be anywhere on iPhone not just iPhone screen. Here is a link which shows that it is possible.

Basically what i want to do is send an alert if user taps 3 times on iPhone while the Phone is in his pocket. What i have achieved is that i can detect the 3 taps but i also get the false alerts as well in these cases. 1) if user walking, 2) waving his phone 3) running. I need to just check if user has hit his iPhone 3 times.

Here is my code.

- (void)accelerometer:(UIAccelerometer *)accelerometer
        didAccelerate:(UIAcceleration *)acceleration
{
    if (handModeOn == NO)
    {
        if(pocketFlag == NO)
            return;
    }

    float accelZ = 0.0;
    float accelX = 0.0;
    float accelY = 0.0;

    accelX = (acceleration.x * kFilteringFactor) + (accelX * (1.0 - kFilteringFactor));
    accelY = (acceleration.y * kFilteringFactor) + (accelY * (1.0 - kFilteringFactor));
    accelZ = (acceleration.z * kFilteringFactor) + (accelZ * (1.0 - kFilteringFactor));

        self.z.text = [NSString stringWithFormat:@"%0.1f", -accelZ];

        if((-accelZ >= [senstivity floatValue] && timerFlag) || (-accelZ <= -[senstivity floatValue] && timerFlag)|| (-accelX >= [senstivity floatValue] && timerFlag) || (-accelX <= -[senstivity floatValue] && timerFlag) || (-accelY >= [senstivity floatValue] && timerFlag) || (-accelY <= -[senstivity floatValue] && timerFlag))
        {
            timerFlag = false;
            addValueFlag = true;
            timer = [NSTimer scheduledTimerWithTimeInterval:1.5 target:self selector:@selector(timerTick:) userInfo:nil repeats:YES];
        }

        if(addValueFlag)
        {
            if (self.xSwitch.on)
            {
                NSLog(@"X sWitch is on");
                [self.accArray addObject:[NSNumber numberWithFloat:-accelX]];
            }
            if (self.ySwitch.on)
            {
                NSLog(@"Y Switch is on");
                [self.accArray addObject:[NSNumber numberWithFloat:-accelY]];
            }
            if (self.zSwitch.on)
            {
                NSLog(@"Z Switch is on");
                [self.accArray addObject:[NSNumber numberWithFloat:-accelZ]];
            }

        }
    //}
}

- (void)timerTick:(NSTimer *)timer1
{
    [timer1 invalidate];
    addValueFlag = false;
    int count = 0;

    for(int i = 0; i < self.accArray.count; i++)
    {
        if(([[self.accArray objectAtIndex:i] floatValue] >= [senstivity floatValue]) || ([[self.accArray objectAtIndex:i] floatValue] <= -[senstivity floatValue]))
        {
            count++;
            [self playAlarm:@"beep-1" FileType:@"mp3"];
        }

        if(count >= 3)
        {
            [self playAlarm:@"06_Alarm___Auto___Rapid_Beeping_1" FileType:@"caf"];
            [self showAlert];
            timerFlag = true;
            [self.accArray removeAllObjects];
            return;
        }
    }
    [self.accArray removeAllObjects];
    timerFlag = true;
}

Any help will be really appreciated.

Thanks

Answer 1

Here is how i achieved it.

- (void)accelerometer:(UIAccelerometer *)accelerometer
        didAccelerate:(UIAcceleration *)acceleration
{
    if (pause)
    {
        return;
    }
    if (handModeOn == NO)
    {
        if(pocketFlag == NO)
            return;
    }

//  float accelZ = 0.0;
//  float accelX = 0.0;
//  float accelY = 0.0;

    rollingX = (acceleration.x * kFilteringFactor) + (rollingX * (1.0 - kFilteringFactor));
    rollingY = (acceleration.y * kFilteringFactor) + (rollingY * (1.0 - kFilteringFactor));
    rollingZ = (acceleration.z * kFilteringFactor) + (rollingZ * (1.0 - kFilteringFactor));

    float accelX = acceleration.x - rollingX;
    float accelY = acceleration.y - rollingY;
    float accelZ = acceleration.z - rollingZ;

    if((-accelZ >= [senstivity floatValue] && timerFlag) || (-accelZ <= -[senstivity floatValue] && timerFlag)|| (-accelX >= [senstivity floatValue] && timerFlag) || (-accelX <= -[senstivity floatValue] && timerFlag) || (-accelY >= [senstivity floatValue] && timerFlag) || (-accelY <= -[senstivity floatValue] && timerFlag))
    {
        timerFlag = false;
        addValueFlag = true;
        timer = [NSTimer scheduledTimerWithTimeInterval:1.5 target:self selector:@selector(timerTick:) userInfo:nil repeats:YES];
    }

    if(addValueFlag)
    {
        [self.accArray addObject:[NSNumber numberWithFloat:-accelX]];
        [self.accArray addObject:[NSNumber numberWithFloat:-accelY]];
        [self.accArray addObject:[NSNumber numberWithFloat:-accelZ]];
    }
}