Monitoring - How to monitor a website for free with email/sms

There is an interesting website that give opportunity to monitor external websites and get immediately email alerting.

I think that screesnhots is quite enough to explain service:

[update 2019.01.05]

While does a good job, it's not really user-friendly and doesn’t work quite fast.
I did some exploring and found the other tool below. It's ad-free, quite straightforward and fast to load and I wanted to suggest you show it alongside the other one:

This tool allows you to check if your website is down across the globe or only on your computer screen, and it’s quite quick and easy to use (and it's completely free, too!) : -)

[update 2020.07.03]

Here it is another website with similar monitoring free features.