Battery Junction sells these for $1 each or sends you one for free with any $20 order:
https://batteryjunction.com/titanium-keylight-colors
They look like generic and slightly crappy 2xCR2016 keychain lights of the type pioneered by LRI/Photonlight and its users. The intriguing thing about them is the mention of a microcontroller. Its purpose is to give click-on click-off functionality that I guess is more convenient, or maybe lower costs by using less precise plastic molding than the Photon II and its mechanical switch requires. But of course it makes me think of running Anduril in the light ;).
The product page has decent pictures of the assembled light, so I have posted a crappy photo of the disassembled light and its PCB. The MCU is the little potted chip-on-board thing. It might be possible to replace it and painstakingly rewire the PCB traces, or else possibly make a new PCB. The pushbutton itself is a little spring contact in the center of the board, going to an MCU pin. I haven't tried to measure the idle current drain. There is another SMT component on the board that I don't recognize. It's about 2mm*3mm and is thicker than I'm used to for SMT resistors, and it's marked "W4". A capacitor? Inductor? Hmm.
There is no PWM and no multiple modes, just on-off. I haven't yet disassembled a Photon Freedom to see if that has more parts inside.
Changing or reprogramming the MCU in this thing is probably not practical, but the electronic switching is interesting in its own right. Another idea that I had is to replace the led with one with full length leads that could be bent to 90 degrees, making a right angle light that could be used as a tiny headlamp. That is not really possible with a Photon II or clone ("Fauxton"), because those use the flexing LED lead as the on-off switch.
In fact I got about 3 feet of sticky-back Velcro at Daiso for something like $1.50. So that suggests a truly tiny headlamp with no strap. Just stick a velcro dot on the back of the right-angle light, and a bigger velcro dot of opposite "polarity" on your forehead, and plop the light there or remove it as needed. The idea is for the velcro to stay on your forehead like a band-aid through an outing of up to a few days, while not causing too much skin irritation. But, I have not tried this crazy scheme ;).
