Lights using a 18650 seem to be the rage these days, at crazy cheap prices, but they all use some UI with clicks, holds, etc.

I have an Olight Seeker Pro 4 and it’s pretty simple to use. The on/off button rotates and controls the intensity. You do have to either hold it for a few seconds to turn it on or rotate the button 90º and then click but that’s unavoidable with these kinds of flashlights.

These lights are very small and yet very powerful. That means you can easily pocket them, but because they are so powerful they also get very hot. You don’t want a flashlight like this to accidentally turn on while in your pocket. If you look at these lights, the head is almost always ribbed, it’s basically a heatsink. Even then when you run them at full strength they usually throttle themselves down after a few minutes to prevent overheating.