Moister Sensing monitors the moisture level and it's going to adjust the remaining time as needed to so as not to over dry the clothes. Once drying is finished it should imediately progress into the wrinkle gaurd/rid cycle. It's important to remember that it won't be able to be 100% accurate since different clothes dry differently, but it is without a doubt a better method to use rather than the old timed drying with guess work :)

I don't do Sears service but I think your model has 2 little strips of metal about 4 inches long and about 1 inch apart from each other. Take a little scrubby pad and some window cleaner and scrub these sensors. They get a little fabric softener build up on them and it reduces the sensitivity of them. As stated by jamesk these strips are to pass a low level of electricity through the clothes when they are wet. Once they are dry the strips can no longer pass electricity so the dryer starts is shutdown cycle.
Other things to check are your exhaust vent to make sure it is clear and it's also a good idea to actually wash your lint filter about every 6 months to make sure it is not getting plugged. It may look clean but can have reduced air flow. I clean them with dishsoap and use my fingers to scrub the screen. Rinse and dry it completely before putting it back into the dryer.
I hope this helps.

My experience shows the answer to the question "How do they work" is "Not very well". Our previous Whirlpool did a fairly poor job of determining when they were dry, but it was an older EM unit.

I know on in our brand new Duet, even though it is set for "more dry", the clothes still have a level of dampness to them when it is "done".

I'm guessing there is a "secret service man button combination" that would let me adjust what I feel is "more dry". Too lazy too look again, but I thought I read that somewhere.

There are two kinds of "moisture" sensors used in dryers.

The older/cheaper technology-type works solely by temperature and mechanical controls. This is sometimes called "thermostat auto-dry." When the heating element (or gas burner) is ON, the machine's timer is OFF ... that is, the timer is stalled and doesn't advance. When the heat source turns OFF, the timer turns ON and begins advancing toward end of the cycle. A simple heat-on/timer-off and heat-off/timer-on control system. Wet clothes and evaporation of moisture tends to keep the air temperature inside the drum down, so the heating source runs more often or for longer periods of time, and the timer runs less. As the clothes dry, the heating source runs less to maintain the target temperature (125°F or 135°F or 155°F or whatever it may be), and the timer runs more, so it advances more quickly toward end of the cycle.

The other method uses an "electronic" sensor, which is just a low-voltage feedback circuit as jamesk describes above, and is usually called "moisture sensing auto-dry." This method can be used with either mechanical controls or fully electronic controls. With mechanical controls, the feedback circuit serves the same function of stalling the timer motor when moisture is sensed, and allowing the timer to run when no moisture is sensed. As the wet clothes tumble and brush against the sensor bars, the timer motor rapidly turns on and off, so it doesn't advance very quickly. As the clothes dry, less stalling of the timer occurs, so it begins advancing more quickly toward end of the cycle. With fully electronic controls, basically the same thing happens with the electronic control software and timing algorithms advancing the cycle toward Off.

Machine with mechanical controls and an "electronic" moisture sensor generally (but not always) tend to be a bit less accurate and less consistent in performance than dryers with fully-electronic controls and a moisture sensor. A mechanical timer coupler with a moisture-sensor MUST travel the physical distance from its starting point in the cycle to the off position. If loaded with dry clothes, they tend to run a bit longer than machines with electronic controls, which can more quickly determine that the clothes are already dry and shut off.

But to more directly answer bmgeorgo's question, yes it's quite possible for the machine to keep heating for a while longer than really needed. Some of these auto-dry machines are oriented more toward *drying* the clothes, and some are more conservative in the target dryness levels. One just has to get accustomed to the quirks of the machine. If you find that the "Regular" dryness setting is too dry for particular loads, experiment by setting the controls more toward the "Less" dry end of the scale. Simple as that!

CluelessHusband, some of the Whirlpool Duet models (and possibly other machines in the Whirlpool family, and other brands as well) DO have a hidden service adjustment to orient them toward drying a bit more. If you are feeling adventurous, most all appliances nowadays have a tech sheet stashed inside that outlines diagnostic routines and service tips. The sheet typically is folded or in a plastic bag, taped inside the control console or behind a removeable rear or front panel. Not ALL adjustment and diagnostics are on the sheet however, just those that may be useful under normal circumstances to a service tech out in the field. There are also numerous downloadable service documents for Whirlpool products at http://www.servicematters.com. But use them at your own risk!

My model has the two thin metal strips next to the lint fiter that jakvis described, and it also uses a mechanical timer. From what I've read in these responses, it sounds like the moisture sensor is working as it should. I clean out my lint filter after every load and my dryer duct once a year, and I never use fabric softener or any additives that could gum things up. I was mainly wondering if I really understood what to expect from the sensor, and how much of a difference it should make on our utility bills.

The savings on your utility bill will be that the dryer shuts off when the clothes are dry and won't be over dried.
In other words If the sensor detects the clothes are dry after 30 minutes the dryer starts it's shut down process.
In time dry if you had the timer set for 45 minutes and the clothes were dry in 30 you have "wasted" 15 minutes of power and gas not to mention the extra wear on the clothes.
I always recommend the auto dry to my customers. I tell them let the dryer figure it out instead of you making an educated guess.

Needed help on the moisture sensor got what I needed Great