Pedometers use a pendulum device that swings back and forth to measure the users hip movements, which makes them very inaccurate. The Shoe Odometer uses a omnidirectional motion sensor similar to an accelerometer. Timex uses a similar mechanism in their running computer. I used the motion sensor, because I found it as accurate as a accelerometer, but it used a fraction of the power. The Shoe Odometer is designed to last 6 to 10 years on one battery.
runskellyrun, stride rate is calculated over the entire duration of your run. It samples every 15 seconds, if it is a good sample it includes the sample in the over all average of the run. Two seconds after the sample, if it doesn't document a step, it throws out the prior sample. By sampling in this fashion, it makes determining the stride rate very accurate. If you stop for a light or any other reason those samples are not included in the over all average.