I remember seeing these propane-powered mosquito traps at local big-box
hardware stores a few years ago, but I don't think I've seen any of them
lately. They retailed for around $300 and up to $450 if I remember
correctly. Some brand names include Skeeter Vac and Mosquito Magnet.

The premis is that they gave off a carbon-monoxide (or co2?) scent (by
burning propane) which would attract mosquitoes into a one-way bag where
they'd die. Some of the claims were that one unit was good for about an
acre of coverage.

The reviews on Amazon are mixed. Some claim it catches everything but
mosquitoes, some claim it works great on them. Many don't like the
ongoing cost of replacing sticky paper.

Some employ some combination (or all?) of these methods: heat, co2,
octenol, lactic acid, suction, blinking lights, sticky paper.

What's the verdict on these things? Are they effective?