Anyone know of any affordable stand-alone sensors to warn you if the water level in your tank/sump is too high? I'd like to add some sort of sensor to my sump so just in case I'm not paying attention during a water change I've got an alarm that would warn me when the water in the sump is too high before it overflows and causes a flood. I know some of the fancy Neptune and Apex controllers have add on modules that do something like this but I was wondering if there were any cheap alternatives out there.