My latest project took me about 15 minutes to make, and is about the size of my thumb, but it's one of the things that gets the most use of everything I've made, and it can't really be store bought.
Well, not cheap at least. My husband runs, and he uses the iPod pedometer (http://www.apple.com/ipod/nike/). There is an attachment to the iPod and a sensor that is supposed to go inside of these specially designed Nike running shoes that have a slot for it.
However, Nerdy Husband doesn't like the Nike shoes in that line, so our DIY spirit kicked in and we figured that we'd find some other way of attaching the sensor to the shoe. NH found an article with a hack for it.
So the version 1.0 was born. It's essentially a tube knit around the sensor. In my infinite wisdom I decided to make in in 2x2 ribbing, out of Lion Brand Microspun. It was ugly, as this was B.S. (Before Socks) and I was unfamiliar with the figure eight cast on, and the yarn and ribbing were bad choices. It was sewn onto the shoe, so in order to take it off, he had to unlace his shoes.
It's pretty wonky, but it's functional. Unfortunately, the sensor is knit into the tube, so when the battery of the sensor died last week, NH asked me to make him another cozy. This led to Version 2.0, which is infinitely better.