How to count service-down with formula KQL

Elastic Observability Synthetics
1

Hey there,
I am trying to collect monitor event with timeout reached. Heartbeat, according with official docs, will create a service-down.

Is there a way to count them?
Something like:

count(kql='http.response.status_code = empty') / count()

2

solution:
count(kql='NOT http.response.status_code: *') / count()