I owned a Sears Demand type water sftnr for 15 years.
The first one i had was a manual, where i had to set the days, Sun. Mon. Tues..., for when it would regen.
Now they have the Demand type, there is an impeller in the inlet side to the unit that spins, and a microprocessor calculates the gallons thru the unit and then will auto. regen next morning at 2:00am (or the time you want.)
The past two years of a 10 year old unit has given me fits. I've ordered repair parts from Sears(thru internet) and have spent approx. $200. Ironically it has now stop working again, typ. it is a piece of dirt or something that gets stuck in a orffice, within the valve area.This piece came thru the city water system. I've replaced the Resin Beads, expensive.... $100+. Probably will need to after 10 yrs. of service. Sometimes you get a Salt Bridge, where the salt forms a bridge , and doesn't drop to the bottom where the water meets and forms BRINE (a salt water solution). Just get a broom stick and poke / break up the bridge.
I'm looking into a No Salt System. haven't got far yet. Have you.
When it works it's GREAT.
I'll probably go out there tonight an look for something (a pain after awhile!)