Hello - I have an application where I wish to detect my movement over ground (asphalt, dirt, grass, snow, etc.). I need non-contact measurement from about 3 feet off the ground. I am not concerned with speed or distance, just the fact that I am moving. I thought of an accelerometer, but I need it to continuously output a signal the entire time I am moving and stop when I stop - similar to what an optical mouse does when you move it over a surface. I've thought of using ultrasonic sensors or even PIRs, but I don't think they will give me the results I want. Possibly a laser pointer aimed at the ground, but what would I use to sense the scattering when I move? I don't think a vibration sensor would work as there are too many things that could trigger it falsely. Anyone have any suggestions? Thanks!