PagerDuty
www.pagerduty.com/tour/mobile-alert-response
From the page
Saved with the link. Notes from 2007 to 2016 are mostly the page's own words, so this is probably an excerpt.
PagerDuty doesn't just alert you of problems using SMS and phone calls it lets you take action directly from your mobile phone. The on-call engineer has the option to acknowledge, escalate or resolve a triggered incident by replying to the alert SMS, or by pressing a key during a phone alert.