A simple price level alert

[Book]

This basic alert differs from built in alerts by being set within a chart; it draws a line at the alert level. You can also pause the
klaxon so it doesn't yell constantly.

/* PriceAlert.efs  -- sound when a price is touched.
    Use Edit Studies to set price.
    Set Pause to numSeconds to wait between sounds.
    Don't setComputeOnClose--it may skip your price.
*/
function preMain() {
    setPriceStudy(true);
    setStudyTitle("PrAlert");
    setCursorLabelName("PrAl", 0);
}
var lastAlertTime = null;
function main(numPrice, numPause) {
    if (numPrice == null) numPrice = 0;
    if (numPause == null) numPause = 0;
    var t = null;

    if (close() == numPrice) 
        t = getValue("rawtime");
        if (t - lastAlertTime > 60) {
            Alert.playSound("train.wav");
            lastAlertTime = t;
        }
    return numPrice;    
}