var seconds = 70; 
            var alarm1 = 60;
            var alarm2 = 30;
            var alarm3 = 10;
            
            var int = window.setInterval("countdown()",1000);

            function countdown(){ 
                seconds--; 
                var count = document.getElementById("count"); 
                count.innerHTML = seconds;
                if (seconds <= alarm1)  {   count.innerHTML = "<span id=alert1>" + seconds + "</span>"; }
                if (seconds <= alarm2)  {   count.innerHTML = "<span id=alert2>" + seconds + "</span>"; }
                if (seconds <= alarm3)  {   count.innerHTML = "<span id=alert3>" + seconds + "</span>"; }
                if (seconds == 0){                    
                    window.clearInterval(int);
                    // window.location = "location";
                    count.innerHTML = "Finished!";
                }
            }

var seconds:  set this to what you want the count down to start at.
var alarm1 etc:  set these values to your thresh hold values 

in either a style tag, or css file, define how you want the appearance to be with the tags of:

alert1
alert2
alert3.

<div>&nbsp;</div> gets placed where you want the counter.

Enjoy.

CountDown with Thresh-holds

JavaScript