On my connected device, i have a bit of code that sends an alert to a server through a bananaPi when battery is low

if ([batt_level] < batt_min){
this.emit('Battery Alert', msg)
}

Alert is then sent to the server and if it registers successfully to the database, it will be sent to the mailer so the user can get a notification that they need to charge their devices:

battery.js:

connection.query(stmt, [body.tag], err => {
      if (err) {
        res.status(400).send("battery can't be registered")
      } else {
        try {
          mailer.sendMail(body)
          res.status(200).send("battery was registered")
        } catch (error) {
          res.status(400).send("an error occured")
        }
      }
    })

mailer.js:

  async sendMail(message) {
    try {
      await this.transporter.sendMail(
        {
          from: process.env.MAIL_FROM,
          to: process.env.MAIL_TO,
          subject: `Alert on device ${message.tag}`,
          text: `foo`,
          html: ` </p>`
        }, (err, info) => {
          if (err) {
            console.log(err);
          }
          console.log("response => %s", info);
        })
    } catch (error) {
      console.log(error);
    }
  }

Now when battery gets lower than 10%, it will send 1 email alert and it is fine, but every time data gets sent to the server (5 requests per minute) and the battery is between 10% and 0% it will send a new email until battery goes back higher than 10% and that's my issue.

Is there some sort of a javascript cooldown I could implement to only send the email/alert once and where would it be the best to implement it (on the device, server, nodemailer?)? I basically want to have the sendMail function stop working for a few hours once one email is sent.

But I cannot implement a general cooldown on the sendMail function because there are a 6 different devices that go through the same mailer, so each cooldown would need to be specific to the device.

(I do not want to have a condition that only sends an alert if battery === 10% or if battery < 10% && battery > 9%, in case the charge level drops from 11% to 8% for exemple).

Thanks in advance