For $9.99, Radio Shack sells large-display indoor/outodoor digital thermometer that are great for use in aquaria. They don't have an alarm, but they are easy to read and reliable. All my tanks have one.
My fish was a female blue ram. I don't know if the temp killed her or if it was how fast the temp rose and fell. My male blue ram for the past week has shown very drab color. Dont' know why, must be sad from loosing his girlfriend