If you want email or text message alerts I would assume that's a complicated enough system you would want uptime alerts on it, and so on recursively ad infinitum.
If you can set up nagios (which one would probably consider an interesting evening challenge if you were already willing to go for your own monitoring droplet) setting up pushover or amazon sns (for sms) should be easy enough.
FWIW, a lot of cellular providers have an email gateway for delivering SMS messages. There's also paid SMS gateways, and options for providing arbitrary push notifications to smartphones.
This was a few (3) years past, but they accepted root@localhost sendmail messages just fine in most cases, and delivered alerts within a minute or two of sending. We didn't rely on this long term, but it was a "good enough" first pass.
I'd probably recommend using one of the gateways (or a more fully-featured service like Pagerduty) for more serious businesses, but for personal use (or where an outage detected the next day isn't crippling), it's remarkably useful.
I would try to set up a completely open source monitoring setup just for fun, but once I'm paying for SNS I personally would rather just pay epsilon more and buy/rent the whole system. I get that may just be personal taste. I absolutely don't trust myself to run my own highly-reliable mailserver to send status alerts.
