Detecting phone shakes

Question

I am developing shake detecting on Android and I can not deal with one issue - rotating the phone. My algorithm detects shakes properly, but it reacts to rotates also.

It looks like this:

//for every second
if(!alarmed) {
    if(Math.abs(oldX - acceleration.x) > threshold || 
    Math.abs(oldY - acceleration.y) > threshold || 
    Math.abs(oldZ - acceleration.z) > threshold) {
        // shake detected
    }
}

oldX = acceleration.x;
oldY = acceleration.y;
oldZ = acceleration.z;

It's JavaScript, because I write with Cordova.

Any help would be appreciated.

Answer 1

After few hours, I came up with solution:

Instead of comparing all three acceleration dimensions with threshold, we should compare sum of all three with (modified) threshold. It prevents reacting to rotations.