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    <p>From my <a href="http://infinite-labs.net/diceshaker/" rel="noreferrer">Diceshaker</a> application:</p> <pre><code>// Ensures the shake is strong enough on at least two axes before declaring it a shake. // "Strong enough" means "greater than a client-supplied threshold" in G's. static BOOL L0AccelerationIsShaking(UIAcceleration* last, UIAcceleration* current, double threshold) { double deltaX = fabs(last.x - current.x), deltaY = fabs(last.y - current.y), deltaZ = fabs(last.z - current.z); return (deltaX &gt; threshold &amp;&amp; deltaY &gt; threshold) || (deltaX &gt; threshold &amp;&amp; deltaZ &gt; threshold) || (deltaY &gt; threshold &amp;&amp; deltaZ &gt; threshold); } @interface L0AppDelegate : NSObject &lt;UIApplicationDelegate&gt; { BOOL histeresisExcited; UIAcceleration* lastAcceleration; } @property(retain) UIAcceleration* lastAcceleration; @end @implementation L0AppDelegate - (void)applicationDidFinishLaunching:(UIApplication *)application { [UIAccelerometer sharedAccelerometer].delegate = self; } - (void) accelerometer:(UIAccelerometer *)accelerometer didAccelerate:(UIAcceleration *)acceleration { if (self.lastAcceleration) { if (!histeresisExcited &amp;&amp; L0AccelerationIsShaking(self.lastAcceleration, acceleration, 0.7)) { histeresisExcited = YES; /* SHAKE DETECTED. DO HERE WHAT YOU WANT. */ } else if (histeresisExcited &amp;&amp; !L0AccelerationIsShaking(self.lastAcceleration, acceleration, 0.2)) { histeresisExcited = NO; } } self.lastAcceleration = acceleration; } // and proper @synthesize and -dealloc boilerplate code @end </code></pre> <p>The histeresis prevents the shake event from triggering multiple times until the user stops the shake.</p>
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    1. POHow do I detect when someone shakes an iPhone?
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    1. CONote I have added an answer below presenting an easier method for 3.0.
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      1. USKendall Helmstetter Gelner
    2. COWhat happens if they're shaking it precisely on a particular axis?
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    3. COThe best answer, because the iOS 3.0 `motionBegan` and `motionEnded` events are not very precise or accurate in terms of detecting the exact start and end of a shake. This approach allows you to be as precise as you want.
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