For each metric you have selected in the realtime overview, you can set a threshold. Thresholds help draw your attention to metrics exceeding your established limits. You can then set up Slack notifications whenever these thresholds are breached. Read more here:

2.https://support.assembled.com/hc/en-us/articles/29550059633037-How-do-I-customize-my-notifications#h_01JXE6YW2SP8Y0ERFV2N1T2YVV