When calibrating a skulk sensor to not hear footsteps, it gives you the "sneak 100" advancement even when you would not power the sensor were you not sneaking.

this can be reproduced by:

1. placing a calibrated skulk sensor and putting a comparator pointing to it
2. putting a redstone torch next to it so that the comparator outputs a signal strength of 15
3. making sure you don't have the advancement sneak 100, and then sneaking next to it

notice that if you were not crouching, you wouldn't power the skulk sensor, so this would not get the essence of the advancement, which is that by sneaking you dismount the alarm.