Its not often I can say a free hosted product can give you alerts and all the info you wanted, but this one does.
I was using the service Monitor.us which is excellent to monitor public site and endpoints. However for free version had a limitation of only 2 systems so I had to resort to making phony email accounts if / when I needed to monitor more than that.
Needless to say it only checked ever 30 min’s and well that didn’t fit my requirements.
Enter UptimeRobot
Not only does UptimeRobot give you an fantastic service along with a wonderful displayed dashboard, I can set the interval down to every five minutes and even have it send email alerts on change in status,
Oh but wait there is more. It can send you SMS messages, RSS, and even update a twitter feed.
All of the above, for free.
This free version I am using will allow me to monitor up to 50 sites/services.
For more info: https://uptimerobot.com/faq