As a teenager I got a new digital watch for xmas. It worked great up until April, when it would mysteriously switch off every now and then. pressing a button would start it up again, but with everything set to zero. This occurred more and more frequently until the summer, when I realised that direct exposure to the sun was the cause. I had to put a black piece of fabric over it for the rest of the summer and got a new watch the following year that wasn't a vampire.