Today, we were working with them. You have to mount them next (on the outside, not inside) to the gear or sprocket that you are trying to count. You need to have the bottom of the geartooth sensor a few mm away from the teeth, but make sure that it doesn't hit the gear or sprocket since it might damage it...and that'd be bad.
http://www2.usfirst.org/2006comp/Spe...oth_Sensor.pdf
Also, next time, search before you post:
http://www.chiefdelphi.com/forums/sh...ght=gear+tooth