This Tessel project pings a URL and causes an alarm light to run continuously if the status code is not 200.
If your website goes down, you want to be the first to know.
Make it obvious when there's a problem by hooking up a big alarm light to a Tessel, which will ping your website every few seconds to check for trouble.
Light patterns
Continuously off: all is well
Continuously on: website being monitored is down
Two-second bursts (on or off): system error; monitoring isn't working (reset the Tessel)