How to check atleast one checkbox is checked in multiple checkbox

In my form so many check-box used now i want to check atleast one checkbox is checked

<div id="sun">
                <li><?php echo $this->__("SUN");?> </li>
                <li><input class="allday" type="checkbox" name="availableday[Sunday][9-12]" value="9AM - 12AM"></li>
                <li><input class="allday" type="checkbox" name="availableday[Sunday][12-6]" value="12PM - 6PM"></li>
                <li><input class="allday" type="checkbox" name="availableday[Sunday][6-9]" value="6PM - 9PM"></li>
            </div>
            <div id="mon">
                <li><?php echo $this->__("MON");?> </li>
                <li><input class="allday" type="checkbox" name="availableday[Monday][9-12]" value="9AM - 12AM"></li>
                <li><input class="allday" type="checkbox" name="availableday[Monday][12-6]" value="12PM - 6PM"></li>
                <li><input class="allday" type="checkbox" name="availableday[Monday][6-9]" value="6PM - 9PM"></li>
            </div>
            <div id="tue">
                <li><?php echo $this->__("TUE");?> </li>
                <li><input class="allday" type="checkbox" name="availableday[Tuesday][9-12]" value="9AM - 12AM"></li>
                <li><input class="allday" type="checkbox" name="availableday[Tuesday][12-6]" value="12PM - 6PM"></li>
                <li><input class="allday" type="checkbox" name="availableday[Tuesday][6-9]" value="6PM - 9PM"></li>
            </div>
            <div id="wed">
                <li><?php echo $this->__("WED");?> </li>
                <li><input class="allday" type="checkbox" name="availableday[Wednesday][9-12]" value="9AM - 12AM"></li>
                <li><input class="allday" type="checkbox" name="availableday[Wednesday][12-6]" value="12PM - 6PM"></li>
                <li><input class="allday" type="checkbox" name="availableday[Wednesday][6-9]" value="6PM - 9PM"></li>
            </div>

how to validate atleast one checkbox is checked.