Google Sheets script to remind me to take backups of my photo archive. See https://emptysqua.re/blog/backup-reminders-google-sheets/

backups-reminder.js

// in days
var backupFreq = 4;
var offsiteFreq = 14;

function sendError(msg) {
  MailApp.sendEmail("jesse@emptysquare.net", "Backup reminders: error", msg);
}

function isWeekDay() {
  var today = new Date();
  /* 0 is Sunday, 6 is Saturday */
  return today.getDay() != 0 && today.getDay() != 6;
}

function checkReminder() {
  /* Don't remind me on weekends */
  if (!isWeekDay()) {
    return;
  }

  var spreadsheet = SpreadsheetApp.getActiveSpreadsheet();
  SpreadsheetApp.setActiveSheet(spreadsheet.getSheets()[0]);
  var sheet = spreadsheet.getActiveSheet();

  /* find the names of data sets, e.g. ["photos", "system"], from the data column */
  var dataColumn = sheet.getRange(1, 2, sheet.getLastRow()).getValues();
  var data = [];
  for (var i = 0; i < dataColumn.length; i++) {
    var datum = dataColumn[i][0];
    if (datum == "data") {
      continue;
    } else if (datum.length === 0) {
      break;
    } else if (data.indexOf(datum) === -1) {
      data.push(datum);
    }
  }

  if (!data.length) {
    sendError("couldn't find any data sets");
    return;
  }

  /* determine the most recent backup, and most recent offsite backup,
   * of each data set */  
  var warnings = [];

  /* for each data set, e.g. "photos" */
  for (var i = 0; i < data.length; i++) {
    var datum = data[i];
    var backupsRow = 1;
    var found = false;
    
    /* find the row with the data set's most recent backup dates */
    for (; backupsRow++; backupsRow < sheet.getLastRow()) {
      if (sheet.getSheetValues(backupsRow, 1, 1, 1)[0][0] === datum) {
        found = true;
        break;
      }
    }
    
    if (!found) {
      sendError("couldn't find backups row for data set " + datum);
      return;
    }
    
    var lastBackup = sheet.getSheetValues(backupsRow, 2, 1, 1)[0][0];
    var lastOffsite = sheet.getSheetValues(backupsRow, 3, 1, 1)[0][0];
    
    if (lastBackup === "#N/A") {
      warnings.push("No " + datum + " backups.");
    } else if (lastBackup > backupFreq) {
      warnings.push("No " + datum + " backups in " + lastBackup + " days.");
    }
      
    if (lastOffsite === "#N/A") {
      warnings.push("No " + datum + " offsite backups.");
    } else if (lastOffsite > offsiteFreq) {
      warnings.push("No " + datum + " offsite backups in " + lastOffsite + " days.");
    }
  }
   
  if (warnings.length) {
    var msg = warnings.join("\n\n") + 
      "\n\n(Intend backups every " + backupFreq + " days, " +
      "offsite backups every " + offsiteFreq + " days.)";
    MailApp.sendEmail("jesse@emptysquare.net", "Backup reminders", msg);
  }
   
};