Instruction: Given a question and the related document, and generate the answer to the question based on the information provided in the document.

Input:
Question: can i add a second unit to get more rooms available to the system ?  will the units be selectable for all channels ?  Thank You ,    Don
Document: The trouble came when we tried to switch 2 or 3 units to channels that Unit-D wasn't on. We used several different channel combinations and got very sporadic results. On one channel A and C could talk but not B. On another channel A and B could talk but not C.  We tried switching D to other channels. This would change the results on the other 3 units, but we couldn't ever get all 3 to talk to each other. The strangest behavior is that quite often A could hear B but B could not hear A.
After a littler over a month one unit craped out and the other three units seem to be going on the fritz. These units are used in a household with only two adults so there is minimal usage and it does not get abused. Thought that I was upgrading from Radio Shack intercom system when I bought this but it was WRONG! I would not recommend this product and would not recommend buying from this seller who will not exchange item  after days 30 Days. BUYER BE WARE! !
These units work ok, but I bought them because I could not get the older style two-wire units to work in every room that I needed. So I was hoping these three-wire units would work in those rooms. They didn't. Our house has a single power meter as required in the product description, but still these units worked no better than the older units. Also, I believe the product description said these unit were &#34;compatible&#34; with the older units. I thought this meant you could communicate from a three-wire unit to a two-wire unit.
This means that, in theory, each outlet would be on one of two different circuits. So, I then tried to get each to communicate with at least one other unit using Solution 1 in the instructions. I could get units to communicate in neighboring rooms since they just happened to be on the same circuit (out of two), but of course that was not useful for our purposes. AS IT TURNS OUT, I COULD FIND NO UNITS ON ONE FLOOR (LEVEL) THAT COMMUNICATED WITH THOSE ON ANY OTHER FLOOR...THUS, THE TWO CIRCUIT THEORY DOES NOT NECESSARILY WORK BETWEEN FLOORS.What finally worked very nicely was to run three prong extension cords down from the top most level from the outlet I wanted to use in the hallway to the next unit in the kitchen, then to the next unit in the family room and finally down to the basement.
This is the ONLY two prong adapter or element of any type used anywhere in the entire system. From that point on ALL extension cords must be three prong and EACH unit must be plugged into it directly (using no three to two prong adapters). As far as I can tell, you are basically tapping into only one two prong line but maintaining communications all the way down by using the three prong connections all the way. Note that you may need to try both the upper and lower two prong line at the initial outlet to get the one that works best.
this intercom was just what i was looking fore, the system i had to replace was over 15 years old,it is perfect,thank you
Note that, for us, this required four extension cords and that each extension cord must end in three outlets into which you plug the next extension and so on down the system. While this required running four extension cords and using duct tape to hold them tightly along on the stairs and across floors as needed, all of the units work beautifully and clearly AND they are exactly where I wanted them to be. Since NONE of my outlets are three prong, the top most unit is plugged directly into a three prong extension cord (using no three to two prong adapter) which is in turn plugged into the original two prong outlet of choice using a three prong to two prong adapter.
I got the 4 unit package,  and they generally work OK.  We have a 7 year old house on a single power meter. We initially had some trouble because we have dimmable CFLs in the house (which ARE hooked up to CFL compatible dimmer switches), which apparently cause significant interference (Yes, just like the guide book says),  when they were off, things mostly worked fine. We'd have a couple issues where on some channels you could hear people in one direction, but not the other. (Yes, the units were all on the same channel).However, when I was researching that actual issue, which isn't mentioned in the troublehsooting section, I started reading the reviews on the product..  and as soon as I saw a pattern in this companies response to ANY post where someone complains,  they are, probably as nicely as they can muster,  calling customers idiots and being condescending to them.So, even though I got this product to work,  I just can't support a company that puts that kind of public faceon their support reaction to customers.I'm sure after this, you'll see a response from them making me out to be an idiot as well.
In summary, this works great frequently and sometimes not at all depending upon which outlet into which you plug a unit.The manufacturer states that it in order for it to work properly, all the units must be installed on 3-wire electrical outlets that are on the same electric meter. Therefore if you're living in a single family residence for which you have only one electric meter and receive only one electric bill, each unit should work on every 3-wire outlet in your residence. NOT SO!!! Although I've found that on some outlets they work just fine but I've, also learned that on some outlets a unit will not send or receive at all, and on others it may only send but not receive or receive and not send no matter which of the four available frequencies you may choose; therefore, be prepared to have to try different outlets in order for a particular unit to work.
Shoddy work on the part of my contractor's electrician and I get angry everytime I fix that &#34;professional's&#34; mistake or laziness. Based on my experience with these units, a bad result is probably a function of poor wiring, specifically the ground. I have one intercom unit in a freestanding 2-car garage some 75' from the house on its own breaker box. That garage shares the same meter as the main house and I wired it myself so I know it was done right. The intercom works perfectly.
Answer: Yes; in fact, we ordered four then added three additional to use throughout the house. All work well together.