The JBJ ATO comes with 2 float switches, and can be be setup in one of two ways. (A or B mode) You can have Both Floats in the Sump. One as a High Level and one Low Level switch (Double the safety factor) This is how I had mine setup.
Or one float in the Sump, one in the Fresh Water Container. This way you won't run your pump Dry.
As was mentioned you can adjust the "RUN TIME" or how long the pump will run before the JBJ cuts power to the pump (You have to open it up and adjust a POT) there is also an Audible Alarm you can enable disable inside
I found that finding the right size pump is the key. (A Toms Aqualifter was TOO Underpowered) The max run time for the Pump is 3 minutes, and the Aqualifter just pumps to slow. I ended up using a MaxiJet 400, and set the max run time at 1min.
So If within 1 minute the Sump is not at the proper level the JBJ Cuts the power to the Pump and goes into fail safe mode. I Figured this way I would never burn out the pump from running dry. OR overflow my Tank/ add to much Fresh Water.
ONLY THING I DISLIKED ABOUT this unit was getting it out of fail safe mode requires unplugging it.
And no Notification of Low Top Off Water on my reef keeper display.
It's now all running on my reef keeper instead, and I'm using DIY pressure switches instead of mechanical float switches. (Cause I'm geeky like that)
For around $100. The JBJ is pretty darn good. and the only reason I switched was because.... Well... errr.... I wanted.... um.... To spend more money !
Just remember to clean the float switches every once and awhile