DRM-114's actual functionality is sort of best described as "optical IRC."
First, attempting anything with RF at DEFCON is an exercise in futility. The noise floor is so high there that anything worthwhile is damn near impossible. Even the conference WiFi is problematic. But IR optical networking should suck a whole lot less (whether it actually does or not... remains to be seen).
So assume that you and a bunch of other folks equipped with DRM-114 and the appropriate dumb terminal are within optical range. Now what?
First, the serial parameters are 115,200 baud, 8N1. The UI will mask off the high bit, so it's 7 bit ASCII only within those 8 bits.
DRM-114 presents a simple prompt:
That prompt indicates that you are in broadcast message mode. Anything you type that doesn't start with a "/" will be sent as a broadcast message and any DRM-114 that manages to receive it without error will print out your name, a ":" and then your message.
Speaking of name... you can change your name with "/n [name]". The badge comes with a default name set - "def_" and 4 hex digits (they're random and based on the controller's serial number, so they should be unique). You can use "/n" without an argument to find out what the current name is. You can change it to anything reasonable (up to 8 printable ASCII characters). There's nothing to prevent multiple users from using the same name. Directed (that is, non-broadcast) messages directed to a name will be received by any and all badges that have that name set.
So how do you send a directed message? You use "/t [partner name]" to set the talk partner's name. If you do that, the prompt will change to
to let you know that the lines you type (again, that don't start with /) will be sent only to that partner destination name.
You can use "/t" by itself to revert to broadcast message mode.
In addition to directed and broadcast text messages, there are also "attention" messages. You send them with "/a". An attention message can be directed or broadcast. It's a directed attention message if you have set a talk partner, and will only be seen by that named partner. If you don't have a talk partner set, then the attention message will be broadcast. An attention message causes the bright blue ATTN LED on the SAO to blink and the message
"[so and so] wants attention!"
to appear. That message is also accompanied by an ASCII BEL character, so if your terminal has BEL support, that'll happen too.
IR networking being what it is, you may find that the occasional message is not properly received (gasp!). If this happens, the "/r" command can be used to repeat verbatim the last message (of whatever kind) was sent.
/h or /? can be used at any time to get help.
Goon special versions have additional functionality, but that's private for goons, so they'll have to figure it out on their own. The help text for goon versions lists the additional commands and should make it easy to figure out.