Today is day 20 and I woke up to three pips. The little unit looses 1.5 degrees at night as my house cools. I don't have central heating in use but use a propane wall unit. It works pretty well but the temp drops two to 3 degrees in the house at night. Last night was a bad one for sleep due to dogs needing to go out so I was able to adjust for the drop at 2 am. I am not sure I would want to go for the full 21 days in this type of unit but it has worked like a charm for me now and in the past.