I keep my unit plugged in all the time, just make sure like others have said to check the batteries water levels.
As for the ultrasonic pest thing. I purchased four of the units have one plugged in the bedroom, outside kitchen, under table with one extra. I also am a believer in moth balls. I do not know if its the ultrasonic or moth balls but I am and have been pest free. I feel they are worth the money.
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S.O.B.
Retired and never looked back
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