That's not a lot to work with. What do you mean by "the feed"? Do you have only one input to Splunk?
Assuming you can define the feed to a specific index (and, optionally, host and/or source and/or sourcetype) then this may help.
index=foo host=bar source=baz sourcetype=foobar earliest=-70m
| stats count
And trigger the alert if the number of results is zero.
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If this reply helps you, Karma would be appreciated.
