Add the javascript mehod given below:

<script>
function capLock(e){
 kc = e.keyCode?e.keyCode:e.which;
 sk = e.shiftKey?e.shiftKey:((kc == 16)?true:false);
 if(((kc >= 65 && kc <= 90) && !sk)||((kc >= 97 && kc <= 122) && sk))
  document.getElementById('divMayus').style.visibility = 'visible';
 else
  document.getElementById('divMayus').style.visibility = 'hidden';
}
</script>

TO call the script from ur control:

<SPAN><input type="password" name="txtPassword" onkeypress="capLock(event)" />
<SPAN><div id="divMayus" style="visibility:hidden">Caps Lock is on.</div> 
 
Modify the script by alert.
 
Hope its helpful for u.
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