Since this is mainly a running blog, most people that read this will be pretty familiar with the Garmin sports watch and heart rate monitor or some other variation. I use the Garmin 405 and I've become so dependent on it, that I have mild anxiety just thinking about running without it.
A friend of mine that is new to running just got one for her birthday from her husband. The very first thing she did was try out the heart rate monitor during sex to see how hard she's working out. True story.