checkbox validation in asp.net using jquery

I am using below script for checkbox validation

Script

 var j = jQuery.noConflict();
j('form').submit(function (e) {
var cnt = $("input[name='chkItem']:checked").length;
if (cnt == 0) {              
j("#chkmessage").html("please checked atleast one");
return false;
}
});

html
<form>
Please select at least one checkbox<br/><br/>
<input type="checkbox" name="chkmessage" value="Test1" /> Test1<br/>
<input type="checkbox" name="chkmessage" value="Test2" /> Test2<br/>
<input type="checkbox" name="chkmessage" value="Test3" /> Test3<br/>
<input type="checkbox" name="chkmessage" value="Test4" /> Test4<br/>
<input type="checkbox" name="chkmessage" value="Test5" /> Test5<br/>
<br/>
<input type="button" id="btnSubmit" value="Submit" />
</form>