They're called Mosquito Magnets and I've had one for about 6 weeks now and it works great. They have units cheaper than $400 though depending on the size of your yard. The only advice I have is to try and figure out if you have the asian tiger mosquitoes or not. The units come with a mosquito attractant that will actually repel the asian tiger mosquitoes. If you have those it's best to not use the attractant and just rely on the unit putting out CO2 and heat to attract them. That's what I've done so far. A quick way to tell if you have the asian tiger mosquito is if you are getting bit in the heat of the day. As far as I know, only the asian tiger mosquitoes bite during the day. I bought mine over the Internet at this site.
FWIW, I had two, sold them both and installed the under-eave system. Maybe we had the asian tigers (Houston - Galleria area) and were repelling them with "attractant", but they never did near the job the new system does (rare to see a mosquito in the yard). Got to be too much of a pain in the *** to keep them up and running full time (changing tanks every 3 weeks and unrealiable on the restart). They were Mosquito Magnets. I'll be interested to hear your results.
BTW, I sold them pretty quickly with an ad in Chronicle classifieds for close to what i paid, so maybe no downside in seeing if you have better luck.
I've heard of some systems that spray cedar oil which will repel mosquitoes but I've never heard of the under-eave system. It sounds interesting though. What exactly is it?
Also, regarding the Mosquito magnet not working, it's important that the unit be placed upwind of the area you want to protect. If you have it in the wrong place, you can actually attract more mosquitoes to where you're at.
Do these things target mosquitoes specifically, or do they basically wipe out all the bugs in the area? I need to do something about the mosquitoes, but I'd prefer not to wipe out everything else if I can help it.
They target bugs that are attracted to heat and CO2. Their web site says that it attracts mosquitoes, no-see-ums, biting midges, black flies, and sandflies. I've noticed a few small moths, mosquitoes and a few million gnats in the net. There are also some strange tiny orange spiders that don't really get trapped but they seem to like to hang around. I guess they feed on the trapped bugs.
The under-eave system to which I refer sprays a combination of pyrethrin (organic) and permethrin (synthetic) from a 55 gallon drum through a system of nozzles lining the eaves of the house and the fence around the backyard. Some people get hung up on the possible residuals left by the chemicals (organic stuff not so much, synthetic stuff somewhat) but in doing the research I got comfortable that it wasn't something I was that concerned about in the concentrations in which I'm using it. You can use all organic but it's more expensive so I mix the two, with the benefit of the slight residual effect from the synthetic stuff. I've found it to be extremely effective.