Acknowledge

Anyone who may change checks can acknowledge in the app; a viewer cannot. The link in an alert works without signing in, for that incident only, and asks for one click first, so a mail scanner that opens links acknowledges nothing.
The first acknowledgement counts. The incident page and its timeline say when it was acknowledged and how (in the app, by the link or through the API).
A resolved incident cannot be acknowledged. Acknowledging changes nothing about the checks: the incident still closes when the site recovers.
A channel that gets one client’s alerts carries the acknowledge link only when you tick Allow acknowledging from this channel when you add it, so a client who reads that channel cannot acknowledge for your team. The link of a channel that was switched off does nothing.

Escalate

On Alerts, add and test the channel that should hear about it: a colleague’s address, an on-call channel or PagerDuty.
Under Escalation, choose Set an escalation rule: the minutes without an acknowledgement (from 5 to 120) and the channel to tell. One rule covers every site; a client can have its own rule, which wins for that client’s sites. A channel that gets one client’s alerts can only be chosen in that client’s rule, so another client’s incident never reaches it.
When an incident stays open and unacknowledged that long, the channel gets one message that says nobody acknowledged it.

During a maintenance window of the organisation, the client, the site or its check.
Once someone has acknowledged the incident, or once it is resolved.
When the rule’s channel is removed or not confirmed: the rule then says why.

Acknowledging works on every plan; escalation rules are part of the Team, Agency and Agency Plus plans.