When you want to deploy Operating Systems zero-touch it can be scary the thought of all systems being added to the collection, so you can it's best to provide as many safe-guards. We currently have a runbook that adds a variable to let the computer go zero-touch however we want to know if there is an influx of computers being added to the collection.
To create an alert -
Right click on the collection and go to properties, then click the Alert Tab
Click Add and tick Member count exceeds threshold
Then customize the Alert requirements based on when you want to be alerted
To get e-mails when an Alert is triggered go to the Monitoring Tab \ Alerts \ Subscriptions and click create new subscription.
Then find your alert based on the collection name.
You may need to also run Configure Email Notification
Emails!