Simple question? Best way to sense light switch being turned on.


New Member
Looking for suggestions on something that I think should be pretty simple but I'm not quite wrapping my head around the "easy" answer... 
Short request...
I just want to provide contact closure when a 120v switch is turned on, what's the easiest way to do that?
Ideally it would be through my Elk so that I can monitor it but I'd be fine with just a relay, etc. that would simply close an N/O connection when I turn on a specific light switch. Eventually I'll want 3-4 of these "inputs" (120v switch) to a single output (contact) which is why I eventually want it to run through the Elk.
More detail...
I've installed an HRV (whole house ventilation system) that has a high speed mode that can be triggered by closing a simple contact. I want to install a standard 120v humidity-sensing/timer switch in the bathroom that would both control a light above a shower and trigger the HRV to kick on. Once the timer switch times out (or shuts off due to low humidity threshold being reached), the contact is open and the HRV shuts off it's high speed mode.
Any simple way to do this that I'm missing? I'm thinking I need the OPPOSITE of an ELK 912 relay (ie sense 120v, trigger contact as opposed to sense 12v and open 120v path). I can't just wire the 120v load of the switch to the +/- of an ELK912 and connect the N/O+Com to the switch on the HRV, can I? I'm assuming the 120v would overload the relay that's expecting 12v, no? I ask because I have a bunch of 912s sitting around. :)
I also have an ISY + Insteon devices in my system that I can work with.
Thanks in advance for any thoughts!
If you have insteon and the ISY, I would think that one of those micromodules with the sense input would be perfect.
Adds a level of complexity that doesn't need to be there.....the sense/timer would be the input to the RIB, which is providing the output. No other logic or device is needed. The light is turned on, triggers the RIB, which then drives the HRV. Switch drops out, RIB drops out, HRV drops out. Simple, just requires some basic wiring.
Can be made even simpler and bypass the Elk by wiring all the RIB outputs NO and parallel for the HRV.
Just install Insteon SwitchLincs wherever you want controlling switches. Let  your ISY decide wen to operate the HRV on cycles or humidity sensing. The switchLinc can be used to control and dim lights using special tap sequences to initiate your HRV, quite easily with a ISY programs.
I am using dewpoint comparisons to decide how long to cycle my HRV from my ISY. It does all the calculations from a 2441ZTH wireless Insteon thermostat and a few other sensing gadgets patched into my ISY.
I also use this ISY controlled technique to decide cycle length for my coldcellar ventilation. It has begun to keep my humidity levels lower than my previous relative humidity and temperature comparisons with much less energy usage.
Bringing in outside air that would increase the humidity was really dumb as most of these HRV units only sense relative humidity and can just waste energy making your A/C take it out again. In some climates the simple humidistat is all wrong and it takes something smarter t do it correctly. ISY can do it and you already have one.