Re: Dumb question, but how do the twisty switches really work?
There are to my knowledge 4 types of twisty light mechanisms, fitting into two categories, and described here to the best of my ability:
1) Tighten head to turn on
A. "Battery-crusher" design, wherein a foam or rubber ring prevents the positive contact of the battery from touching the head circuit board while the light's head is loosened. When the head is tightened, the foam compresses, and the positive, raised contact on the battery eventually makes contact with the head -- which completes the circuit and turns on the light. This design does not usually include a spring in the battery tube, so the battery can rattle if the head is loosened too much. There is also a risk of damaging the battery if the head is over-tightened, thus the colloquial name.
B. "Spring" design (not sure if there is a better name for this), wherein the battery is suspended in the light's battery tube between one or two springs. Differs from "battery-crusher" design in that the battery is always touching the light's positive and negative contacts. The "switch" in this case is actuated when the circuit board contacts the body of the flashlight, again occurring when the head is tightened down. ln this design, the contact board is isolated (insulated) from the rest of the pill, and needs to make contact with the un-anodized ring near the top of battery tube for the circuit to close.
C. "QTC" (Quantum Tunneling Composite) design, wherein a QTC pill is included in the circuit path; when the head is tightened, the QTC pill is thereby compressed. When QTC is compressed, its electrical resistance drops, allowing more current to pass through the circuit and illuminate the LED. This method theoretically allows for infinitely variable brightness between off and max output without the need for advanced circuitry, but in practice some find it "fidgety" and unreliable. In any case, you will generally only find QTC used on custom lights, or from a handful of smaller manufacturers like Peak LED Solutions.
... in all three of these methods, I believe that current needs to pass through the threads at the head of the light to the pill, but there may be exceptions.
2) Loosen the head to turn on
A. The example which comes to mind is the very common Mini-Maglite 2xAA (and Solitaire?) design, wherein a dedicated, spring-loaded switch mechanism OPENS the circuit when the head is tightened down. Loosening the head allows the switch mechanism to expand and close the circuit. I don't know of other lights that work like this besides those offered by Maglite, and I have never had occasion to take one of these switches apart to get a better view of how they work.
I do not claim to be a super-expert... others may know of different twisty light "switch" methods.