function main() {
  // Settings
  var campaignName = "Campaign Name";
  var significantOverlapChange = 0.1; // 10% change triggers an alert
  var lookbackPeriod = "LAST_30_DAYS";
  var recipientEmail = "your_email@example.com";

  // Get Auction Insights Data
  var report = AdsApp.report(
    "SELECT Domain, ImpressionShare " +
    "FROM AUCTION_INSIGHTS " +
    "WHERE CampaignName = '" + campaignName + "' " +
    "DURING " + lookbackPeriod);

  var rows = report.rows();
  var competitorData = {};

  // Store Impression Share Data
  while (rows.hasNext()) {
    var row = rows.next();
    competitorData[row['Domain']] = row['ImpressionShare'];
  }

  // Compare with Current Data (Simplified)
  var currentCampaign = AdsApp.campaigns().withCondition("Name = '" + campaignName + "'").get().next();
  var competitors = currentCampaign.targeting().auctionInsights().get().results();

  competitors.forEach(function(competitor) {
    var domain = competitor.getDomain();
    var currentImpressionShare = competitor.getStats().getImpressionShare();

    if (domain in competitorData) {
      var previousImpressionShare = competitorData[domain];
      var change = Math.abs(currentImpressionShare - previousImpressionShare);

      if (change >= significantOverlapChange) {
        // Send an alert - Customize this part
        var subject = "Competitor Alert: " + domain;
        var body = "Impression share for " + domain + " has changed significantly in campaign: " + campaignName;
        MailApp.sendEmail(recipientEmail, subject, body);
      }
    }
  });
}