My cats were waking me up every night begging for food.  One night my cat licked my eyelid and it hurt my cornea so bad I thought it could be damaged.  I ordered these feeders and they worked like a charm.  I had them go off at the most frequent setting and so that they would get fed in the middle of the night.  I finally got sleep, they lost weight, and they didn't bother me for food because they knew that the feeder was the one that would give it to them.  The only downside is that you cannot have it too close to where you sleep.  It's not obnoxiously loud but loud enough that if it's near your bed it will wake you up.  It takes a nine volt battery that if either store bought or rechargeable will last a month.