WTB Wired Home Intercom, PST.

August 13, 2007 1:22 PM

Our house is undergoing an extensive remodel and I would like to install a wired, press-to-talk intercom between the first and second floors (and the basement as well, if possible). Ideally, I would prefer a solution that draws no power when the PTT button is not pressed. Does something like this exist? At first glance it seems simple to make an intercom that only uses power to drive a speaker on the other end when the PTT switch is on.
posted by turbodog to Home & Garden (8 answers total)

Not a perfect answer to your question, but I have seen DIY systems along these lines, using telephone handsets, that only use battery power when one of the phones is off the hook. (Actually, both the phones?)

The only problem is that although it's trivial to wire two phones together and put a battery on the line so that you can hear each other talking, it's difficult to get the ringers to operate. So the usual method involves rigging up a lightbulb to flash on the other end in lieu of the regular bell ringer. (The system I saw used phones that had a 'voice mail waiting' light and flashed that, I think using a DC bias on the line.)

So it's definitely possible to do. I suppose that as you add more features to an intercom system, it might become necessary to have each station draw some amount of phantom power (also depends on the kind of microphones). But maybe there are some very simple/primitive systems out there, if you don't want to DIY, that are essentially just a "field phone" type system.

Alternately, you could always get a set of sound-powered phones...no batteries required. :)
posted by Kadin2048 at 1:54 PM on August 13, 2007

Also not an exact solution, but large old houses often had tubes that you could talk through. I believe you would stopper the tube with a whistle and when you blew into the tube, the whistle would get the attention of the maid or butler or whoever. You could make them out of PVC easily and they use no power.

Someone over the years removed the tubes from our old house, so we've got a set of cordless telephones that have an intercom feature. Works fine and no duplicate gear necessary. Still, I wish we had the tubes. They're more interesting.
posted by kuujjuarapik at 2:05 PM on August 13, 2007

Well if you prefer an exact solution, aiphone intercoms work this way. Two wire system whereas the base unit is the only powered unit. Typically a 22/4 or a cat5 is ran just for spare pairs. 1 wire per unit. The bases come in a 4 or 8 intercom setup. Typically used more in the commercial world, although they probably have nicer looking residential models.
posted by wile e at 2:45 PM on August 13, 2007

The awesome factor of sound powered phone stations [different link] would definitely be high. Problem is, it works more like a phone, where the callee has to pick up.

You could also leave all the plumbing and wiring exposed outside the walls, and paint everything white and grey to complete the whole warship theme.
posted by ctmf at 3:58 PM on August 13, 2007

Best answer: It doesn't perfectly fit your criteria, but we use a Panasonic phone system throughout the house just for this reason (three story home). Only the base unit plugs into the phone line (although that's not even necessary with this bluetooth version), all the additional handsets link to the base (we have 4 scattered throughout the house), and we can 'intercom' any other phone in the house, as well as carry on multiple phone conversations.

I am not a Panasonic employee
posted by matty at 5:59 PM on August 13, 2007

Wow I put a lot of things in parenthesis (see above)!
posted by matty at 6:00 PM on August 13, 2007

echoing matty - we have a Uniden phone system in our 3-story. If you have power, a cordless phone system is the simplest way to go, and the most flexible.
posted by anadem at 10:34 PM on August 13, 2007

Best answer: Cordless phones with intercom are where it's at.

Short of that, you can buy ultra-cheap power-amp kits that give maybe 1W of power from a single little IC on a tiny circuit board that takes 2 minutes to solder together. Your PTT button is the power switch. Put a speaker (e.g. one half of an old pair of $10 computer speakers), mic and power amp at each end and a CAT5 run will handle the signal.

Like this. Powerable in the long-term with 4-6 alkaline AAs or a $5 plugpack, but the latter would draw non-zero current just sitting there.

Email me if you want more detail.
posted by polyglot at 11:25 PM on August 13, 2007