> I don't know what an SMS is

Short Message Service = cellphone texting

> but that circuit has huge value resistors on it. It should sense
> everything from humidity through fingerprints and flux residue,
> plus any cellphones used nearby. Is there a good reason for
> that ?

Lower power. They make no mention of interference in the article

The only part of the article that needs passing on is the set-up

VR1 is a 25-turn. On their PCB the middle and furthest-from-
the screw terminals are shorted. I don't have one of these and
can't say whether CCW is more or less R

"In order to set the cut-off voltage accurately, you'll need a an
adjustable DC supply, multimeter and a small load, such as 680R
resistor and LED. Hook up the supply to the input terminals and
the load to the output terminals. Initially set the set the i/p V a
couple of V higher than the desired cut-off V

Now wind VR1 fully CCW  and then power up. The LED should
illuminate, indicating the FET has switched power to the o/p

Next monitor the i/p V while you carefully adjust your supply to
the desired cut-off V. That done, wind VR1 slowly CW until the
LED goes out, indicating the FET has disconnected the load

To check the reconnect V, slowly increase the i/p V. The FET
should switch on again at the expected V, illuminating the LED

In use, the cut-off V may vary slightly from that set above due
to the resistance of the fuse, connections and cabling"

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