fping
command.
If all fail you will be alerted. If some but not all locations fail you will receive a warning.
From a link inside every email you can stop the service. Using the service for the first time requires the confirmation of your email address.
If your email is already confirmed you can set up more pingers by just entering the IP address or FQDN of your host. 51.15.121.20
2001:bc8:1828:130a::1
151.115.33.60
2001:bc8:1e00:560e::1
173.255.219.220
2600:3c01::f03c:92ff:fe95:69f4
104.131.19.61
2604:a880:800:14::b6:6000