Pingtower
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Critical alerts
A 3 a.m. page you sleep through is not a page. An escalation is delivered with Apple's critical-alert entitlement, which sounds at full volume through Silent mode, Do Not Disturb and every Focus.
Which pushes are critical
The event decides, not the level. An alert.opened is an ordinary notification. An alert.escalated, meaning a rule’s renotify fired or a ladder rung was reached without an ack, is delivered as a critical alert. So a rule with renotify_minutes: 10 gives you a quiet notification first and, ten minutes later if nobody acked, one that breaks through.
If you want the first page to be loud, give the rule an escalation rung with after_minutes: 1.
Enabling it
iOS asks for critical-alert permission separately from ordinary notifications, the first time the app registers for push. The device reports its own answer to the service, and the service sends the critical rendering only to devices that said yes; every other device gets the ordinary one. If you declined, turn it on under Settings → Pingtower → Notifications → Critical Alerts; the app re-registers on next launch.
Who receives it
Every device of every member of the tenant, unless the escalation rung names schedules or accounts, in which case only those people.