for my setup, the way I touch the DMM is via its digital interface and I'm limited to it being a one-way push. for many, its two-way but you dont really need that. nice to have, but not 100% needed for most tasks.
I'm polling the dmm and getting its value over optical. my esp chip in that opto poller 'head unit' (literally sits on the dmm's head) will listen for espnow pings from the button and it will mark the current (last) value along with an ntp timestamp of the value. log to nvram if you want or echo thru websockets to some remote target, etc.
but that's the overview. a bit of hw that reads a meter and will mark the sample with time when it gets some remote indication.
I've been thinking more about this. do I really want to make a nice probe awkward to hold? I'm struggling to think of some 'clamp on' that wont make the probing annoying to use. also, if you are in a tight area with your probe needle, pressing a button on the probe could very well cause it to slip and short where its not wanted. what I'm now thinking is the better method is a wireless footswitch. it accomplishes exactly the same thing, although less sexy. but way more practical. no probe movement, you use ANY probe you want (I like my probemasters) and the foot switch is 100% wireless so you locate it where you want. comments about that approach? would you use it, if you had some need for this?
the link on amazon on the special button probe is interesting. I might buy one to just see if its usable. I can intercept that button and the hardwork (plastic design) is already done.