That'd be hard to understand how the standing flows were disrupted in the WOS if they worked like that, no?

That sounds more like an alternative way to power up ter'angreal that wasn't used in the standing flows days, but that the Forsaken are using now to power up devices they must keep active for long.

It's more plausible in the AOL this worked with a worlwide network of devices creating a wireless net the ter'angreal could tap the Source through (and that could separate the flows), and only few ter'angreal had this mechanism incorporated instead (possibly the weapons like shocklances, and devices like the Finns portals etc.) or could only be operated manually (anything that involve complex weaves to operate like the BOW, and anything dangerous etc.).

Obviously, there were ways to activate/deactivate a ter'angreal that wasn't involving channelling, if it had access to the standing flows (movement or sound detectors, touching a specific area etc. - just like you described). Of course, these means are useless now, because ter'angreal are rather "jump started" by channelling the proper flow directly into them. Most likely there's something standard in the ter'angreal that could "tell" the SF what flow was required (the ter'angreal don't do this themselves, or they'd auto-select which flow they need whatever you channel into them), and it's likely this can still be "read" into the ter'angreal, but the knowledge how to do that is lost. AS have not found out how to know which flow must be channelled in which ter'angreal. The Forsaken don't seem to have that problem, and with the standing flows it's extremely unlikely they knew by rote how to power manually every mundane device existing - or that every AS knew enough about ter'angreal making to figure out by logic which flows it needs just by its function. They are able to tell, somehow - either just by looking at the object, or more likely with some kind of standard weave that is safe to channel on any ter'angreal and that let you know how to power it.