I think what you are talking about is the John Blue liquid monitoring system.  We have it, and really like it.  It's the same as all of the other systems that use flow balls to monitor the flow through individual tubes, but it uses wifi to send that data to your iPad.  This allows you to see it without turning around or if your view is blocked in some other way.  Also, an alarm goes off when the flow drops below a point you set, so you know when it runs out.  

http://www.cds-johnblue.com/pump-accessories/flow-monitors/liquid-blockage-monitor-system.shtml