Tring to minimize the number of alerts received

[mpilacik]

Hi Everyone. I'm struggling to find a good way to minimize the number of alerts we receive when a site's power is cut or if the site drops their internet connection. I've looked at Event Correlation, I've tried creating a dummy item using these items expressions, but receive errors when creating the Item. I feel like I'm running in a circle. Essentially, what I'm looking to do is have Zabbix recognize when a few devices are offline, quiet the noise and just send one alert that the entire site is down. Additionally, I don't need Zabbix letting me know that every device is back on line.

sum(//HOST GROUP/agent.ping,nodata(5m))
count_foreach(eq(//HOST GROUP/agent.ping,0))
grpsum["HOST GROUP","agent.ping",last]
grpsum["group","icmpping","last","0"]

Error I'm seeing for each:
Incorrect expression starting from "grpsum["group","icmpping","last","0"]".

Any direction could be helpful.

Thank you,
Marc