Hi,
While I agree with you, there should be a way to notify you for critical alerts this can become annoying very fast. For instance if you're in a meeting and you get a critical Pulseway notification and the phone vibrates every 15 minutes it can easily distract you. What we usually do is when we wake up, we see the list of notifications on the phone and we react to them. Our engineers do not use the Do Not Disturb feature so they can react to the notifications as soon as they get triggered.
An alternative would be PagerDuty which can send you a text message or even call you when a certain notification is triggered.
Chris