How to get alerted when your website goes down, without false alarms

A single failed check usually isn't an outage:

• A blip at the checker. The machine doing the check lost its network for a moment, or its route to your server did.
• A slow DNS answer. Looking up the name took too long, so the check gave up before it reached your site.
• A restart. A deploy restarted the app, and for a few seconds nothing answered.

Your visitors didn't notice any of these. If each one wakes you, you'll start muting the alerts, and then miss the real one.

• The status code. The page answers with 200, not an error or a sign-in page.
• A word that must be on the page. A server can answer 200 with an error message or an empty page. A word that's there only when the page works catches that.
• The certificate. A certificate that runs out makes browsers refuse the site. Get a warning weeks before.
• The domain's renewal. A lapsed domain takes everything down at once, email included.

• Confirm from a second place. When a check fails, check again at once from somewhere else, on another network, and alert only if that fails too. This takes out the checker's own blips.
• Wait out short blips, if you like. Alert only if it's still down after a few minutes. You hear about real outages a little later, and about restarts never.
• Two good checks before "up". A site that flaps, up and down and up, shouldn't alert each time. Call it recovered after two good checks in a row.

To do it yourself, run the same check from two servers in different regions, and alert only when both fail:

• Each check comes from one place, taking turns: San Francisco, Frankfurt and Singapore. When one fails, BadgerBell asks again within seconds from the two other places, and you hear about it only if 2 of 3 agree.
• A probe that's having problems is set aside, and its results don't count.
• Back to "working" only after 2 good checks in a row.
• Alert only if it's still down after 1 to 15 minutes, if you like. It starts at 0.
• A website monitor can look for a word on the page, and every website monitor also watches its certificate and domain, which don't count toward your plan.
• Alerts by email, Slack and webhooks on every plan, Free included, and by text on paid plans.
• Free has 10 monitors, checked every 5 minutes. Indie has 50, checked every minute, for $9 a month.