In the year I used it, I never personally noticed it going down. Although that being said, their SLA is only 99.9% delivery in any calendar month within 5 minutes. The penalty for missing that SLA is only 10% of that month's bill.
> Once an Incident is triggered, PagerDuty will deliver the First Responder Alert within the Notification Delivery Period for 99.9% of the notifications sent by PagerDuty for the Customer during any calendar month. The “Notification Delivery Period” is five (5) minutes and it is measured as the time it takes PagerDuty to deliver a First Responder Alert to telecommunication providers in accordance with the Service configuration and Contact Information.
> ...
> If PagerDuty fails to meet the SLA set forth herein, Customer may receive a service credit. Customer will be eligible for a credit toward future fees owed to PagerDuty for the PagerDuty Service. The Service Credit is calculated as ten percent (10%) of the fees paid for or attributable to the month when the alleged SLA breach occurred.
> Once an Incident is triggered, PagerDuty will deliver the First Responder Alert within the Notification Delivery Period for 99.9% of the notifications sent by PagerDuty for the Customer during any calendar month. The “Notification Delivery Period” is five (5) minutes and it is measured as the time it takes PagerDuty to deliver a First Responder Alert to telecommunication providers in accordance with the Service configuration and Contact Information.
> ...
> If PagerDuty fails to meet the SLA set forth herein, Customer may receive a service credit. Customer will be eligible for a credit toward future fees owed to PagerDuty for the PagerDuty Service. The Service Credit is calculated as ten percent (10%) of the fees paid for or attributable to the month when the alleged SLA breach occurred.
https://www.pagerduty.com/standard-service-level-agreement/