If you need to take the pHin Smart Monitor out of the water for more than a few hours, please unscrew the bottom, fill the small plastic cap with water and re-attach the plastic cap to cover the black tube/sensor. Next, re-attach the bottom of the monitor. (And don't forget to remove the plastic cap from the black tube/sensor when you're ready to put the pHin monitor back in your pool or hot tub.)
If you've lost the plastic cap, just try to keep the bottom of the device submerged in water to keep it moist.
If you just want to take the pHin monitor out of your pool or hot tub for a few hours while your kids splash around, no problem, just remember to put it back after they get out of the water.