I know that footguns are broadly "on-brand" for the flipper zero ecosystem, but exposing high-voltage leads like that without any warning whatsoever seems a bit much.
That said, it's always prudent to treat any live electrical line as dangerous unless you know for a fact that it isn't, of course.
It's counterintuitive enough that the probes actually have an "anti-warning" label to inform people that they are safe to touch.
With low voltage battery circuits the main thing you have to be wary of is capacitors because those can push out a lot more current than the battery itself. Usually you can judge how much a capacitor would hurt if you touched it based on its size. If you have a device with 20 batteries charging a baseball sized capacitor, be very cautious (like the DIY gauss guns/rail guns you see on youtube). Even a thimble sized capacitor will jolt you surprisingly hard. One time I touched the charged capacitor of a disposable camera and the discharge gave me quite the zing.
It can still be dangerous though, it can trickle charge an output capacitance which will deliver the current to hurt you. A small battery only charges it more slowly, the end result is a function only of voltage (assuming the battery has sufficient capacity to completely charge the capacitance).
For the sexond, Geigers are binary, they only report detection events, not types. So you don't want it to be triggered on non-X rays like interferences from computers around, and you might also want to be able to occasionally remove surface contaminants from the equipment. Both of these are easily achieved by giving it a durable opaque case which is how everybody do these.
And for the first, I believe a modern photodiode taped over is by itself more sensitive than Geigers, even more so if coupled to a scintillator crystal(salts that glows in x-rays), not to speak of spectrometer based systems that can additionally tell energy levels therefore types and biological damage levels of incoming rays.
The real Geiger tube running on display is cool, but that's strictly it. I believe.
The suggested board is powered by USB, that's 5V 500mA, so, 2.5W. Let's say the tube is run at the recommended 380V, at 2.5W, that's a current of 6.5mA, which is barely painful, and not dangerous. I guess that with that power, if the circuit really wanted to hurt you, it could boost the voltage in the 50-100V range for a ~30mA shock, which is definitely painful and the start of what is considered dangerous. Electric safety is complicated, there is so much to take into account: current, voltage, frequency, location, presence of water, etc... Skin resistance is far from constant.
Maybe it could do more if it disregards the 500mA USB limit to the full 1.2A that the Flipper Zero can deliver, or with capacitors, but it doesn't seem to have enough of them for a significant power reserve. If it could do that, I would also worry about plugging it to my Flipper Zero or to anything of value out of fear of damaging it, as it would have to be of pretty terrible design, but well, that's AliExpress after all.
Yep, and even with AC, it depends on the frequency. There are a ton of variables affecting how dangerous electricity is to people, so it's hard to make general statements about it.
https://www.youtube.com/watch?v=BGD-oSwJv3E
But even beyond that, the maximum power output will still be pretty limited. If you short the HV rails, it will almost certainly start to drop in voltage and raise in current quickly, but only to the limits of the resistance from other elements in series and the power source's output ability. I strongly doubt you could even make something dangerous from the Flipper, at least unless you attach a large cap, let it charge slowly, and attach a taser module.
I would be rather surprised if a device that is powered off a lithium ion battery like the one in the Flipper Zero managed to seriously injure someone.
The thing to remember is the output impedance. You can have 1000's of volts at a node, but its sourced by a VERY high impedance output. so when you touch it with your hands (which is like 100kohm on a dry day), the voltage collapses because of the voltage divider your hand created.
But if the output impedance is low (transmission lines), well its game over.