I've been using Cronitor since spring of 2014 and it's been great. I initially used it to monitor the uptime of the real-time location feed from my local transit agency (so I could email them to fix it). It was pretty remarkable being able to setup monitoring in ~5 minutes with a single line of code. Now I use it for tons of daemons and cron jobs, it's pretty great to actually have them monitored (not to mention the super simple duration tracking).

Once, it appeared that I was getting false-positive alerts so I called the phone number (not really knowing what to expect) and when (Shane I think?) picked up on the first call I was just flabbergasted that someone was available almost immediately to explain my monitor's behavior. (I had conflated the /run ping with the /complete ping). I highly recommend the service based on their support and my good experience with their API.