title: How to check remotely if multiple Raspberry Pis are online (or not) without opening ports on multiple routers?
body: <p>I'm trying to check if my raspberries are online from outside my home but for security reasons I CANNOT open any port on my routeur.</p>
  
  <p>When I'm on the same network, I just ping them with a PHP script but how can I do it remotely ?</p>
  
  <p>I would like to be able to do it with PHP.</p>