Duh i take my phone out to the protest

Would this be difficult to actually put together? Asking as a mostly casual user of technology and of course for purely academic purposes.

Depends if the phone is supposed to still work.
If you just take an empty shell it shouldn't be hard at all to put an USB killer inside.
If you want to keep a functional phone, that's very difficult. You'd likely have to reduce the size of the battery by half to free some space and then design a custom USB killer to fit into that space. And then you need some kind of switch to switch between regular USB usage and USB killer mode. Or you just hard-wire it to USB killer only and charge your phone exclusively with wireless charging.
- Or you just hard-wire it to USB killer only and charge your phone exclusively with wireless charging.
  That feels really insightful.
  Saw this post earlier and was cranking some brain cycles in kinda the same way you were. My brain settled on a switch for the USB since you should just need a 5 pole/2 throw switch (think I'm using those terms correctly?) to go from regular USB function to kill mode. I think for my own peace of mind, I'd want it to be 3 throw though (normal, completely unconnected, and kill). My brain then went to the battery, which I see as the real design constraint.
  Then I got to thinking about building it into a phone case. The case would need to plug in to your phone's USB port, then have an additional external connection; it would be this connection that is switched into normal/nothing/kill mode. Cases can be pretty bulky, so tucking a battery into there would be easier and still maybe evade detection.
  All that said, I think I like your idea better.
  Edit: spelling
  Edit 2: additional thought: if you went with the case, you'd want to have it really difficult to remove. Like, requiring undoing some screws, especially if you can get some torx or other niche screw head design (bonus points for mix and matched screw heads).
  My thoughts on that are that even if the case is identified as having a false port on it, it would be so difficult to remove that the "adversary" just plugs their info stealer into it anyway.
- USB-C has a lot of pins, some custom built cable could use nonstandard pins for power and data and the standard data ones for the 20kV line.
  Or just run the 20kV line on the data pins and leave power standard. That way you can use a power-only cable to charge the phone.
- You have piqued my curiosity. I was imagining a non-functioning device with the sole purpose of hampering USB/devices. Like if I were to, conduct research, I would probably just have the insides filled with sand or something to give it heft or the illusion of being a real phone.
I would like to actually use something like this on the police because they deserve it for illegally attempting to search my phone.

Is this funky looking police tablet a real thing, and if so, what exactly is it doing?

It is a real thing and they are produced by a company called Cellebrite. They are used in digital forensics. So if they get your phone confiscated or whatever, they can plug the funky looking police tablet and hack it.
- Can always rely on Israel for digital forensics tech
It's real! It has a dozen different plugs for different phone models, and it can make a dump of the physical memory of the device, allowing you to read messages, files etc... without having to unlock it.
I used to work for a PI who used it, he was an incompetent piece of shit but the tech was fun to play with.

I have a broken phone with failed glue lying around. Might be a fun weekend project. Is it still destruction of property if you tell them beforehand that your phone will fry their device?

Edit: Well, not fully broken, but the parts to fix it properly cost more than the device. Even though it has a midrange snapdragon and 12 gigs of ram, 256 gigs of storage. Might try to find out whether there's any way to connect the board to a generic screen, but I'd wager there isn't. Really love the mobile device market.

Edit edit: We're getting really off-topic now, but looks like that board used a MIPI DSI connector, I think? Seems like it is standardised enough that it might be possible to source a generic screen and use it kinda like a sbc? Getting that to work might be the actual fun weekend project hiding here.

unreasonable search and seizure might cover that.
- Luckily, I'm not in the US, so that doesn't really apply. But I might look up the relevant laws around here at some point.

Wow. And we mock metal nutsacks on pickups.

Electrifying idea

Intriguingly so.

Just saw the mentaloutlaw video. Graphene OS has a “duress pin” that wipes the phone when given a certain pin.

There is also an app called duress if you don't have graphene
This is really cool, can't wait to get my google pixel.
fun fact, in the UK the offence is “failing to decrypt the device when required to do so” making these measures quite dangerous.
That said, unless you are being charged under a national security crime, the maximum sentence for “failing to decrypt the device when required to do so” is up to two years, so the game’s the game.
- I wonder how they'd look at it if previous cracking attempts wiped the device. Is that "failure" to unlock punishable or not? The phone was wiped already - the user can't unlock it even if he wanted to.
  Similarily, is it possible to make it impossible to prove the device was wiped due to the PIN and not beforehand?
- What the fuck. When are you required to do so?
- Wow the UK is a turd too.
I still dont know if i would trust Google hardware. Call me paranoid but what are the chances of mentaloutlaw beeing a psyop "get this very specific hardware and software setup so the police cant hack you" sounds a lot like encrochat.
- Have a read up on GrapheneOS, they seem like they take their shit very seriously and their product is pretty solid (though their communications are a bit... "opinionated"). And yes, it is an amusing irony that the most secure devices are made by Google.
For awareness you can achieve the same on CalyxOS by setting it to automatically wipe the phone after either 5 or 10 failed unlock attempts. Though this does mean a child (or childish friend) could do it accidentally. I'd prefer a duress PIN, but then I'd probably forget it if I ever really needed it.
There's also a less nuclear 'panic trigger', that allows you to hide apps or choose to uninstall any apps you like. No PIN needed, simply hold the power button and select 'Panic Trigger', there's then a fullscreen 5 second countdown before your select private/sensitive data is obliterated.. unless you hit cancel. The user can set up in advance what the panic trigger does - eg which apps to uninstall (deleting their data and auth keys), all cloud provider apps with sensitive data such as email apps or cloud storage provider apps are recommended.
- For the duress PIN, an easy way to remember it would be to reverse your regular PIN
Sounds like they would do you for destruction of evidence.
Holy based
Now that's a good idea!

I just had this thought today lol. Either that or loading some malware onto the phone that executes on USB connection.

This person edited their comment.
They originally were talking about giving immigrants moving to the United States USB killer devices in order to unknowingly trick ICE officials.
+++
They get caught with them, fry an ICE machine (as you intended) and get deported to a concentration camp.
Congratulations.
Let’s not use people as a means to an end.
- Aren't the people ICE kidnaps being deported to concentration camps regardless? So the frying of an ICE machine is purely a value-added service.
I mean, this is just general patriotism I think
Very "Don't tread on me."

Imagine dropping USBs in different shells and handing them out to migrants