Which line are you riding on? I take BART from Dublin/Pleasanton to New Montgomery every day and the only time I lose my signal is through the Lake Merrit tunnel and Transbay Tube.
I mainly commute between the city and Berkeley. The signal obviously goes dead in the transbay, but it's been pretty spotty in the above-ground parts, too.
(Not that I think that $10 is reasonable for a day pass.)