Reliability

One of the ways to assess the reliability of the Alarm service is to check the Reliability Canary. This is a contract which continually reschedules a call to itself every 480 blocks (approximately 2 hours). If any of these function calls is ever missed the canary dies.

http://canary.ethereum-alarm-clock.com/

A dead canary means that at some point one of the calls that the canary scheduled was not executed.