Bests & Worsts Reviews from Amazon

As others have pointed out, this is NOT the old thermostat you've seen for the last 50 years. The CT87K, CT87N, T87K and T87N are recent updates. The old thermostats relied on a coiled bi-metallic strip and a mercury switch. The new ones have done away with the mercury with its disposal headaches and replaced it with an electronic sensor and switch. I can't speak to the accuracy of the electronic switch (they're usually accurate to one degree F), but of three I had sitting in a box by my desk, two showed temperatures within one degree of each other and one was off by 3-4 degrees. That's a problem if you're relying on the display thermometer to set a comfortable temperature on the thermostat. Then there's the battery. They don't tell you about the battery, not even in the user manual. If you poke around long enough, you can find a reference to it on the Honeywell web site. It's a lithium CR2450. They seem to be recharging it from the low voltage wires to the thermostat, but even then, it doesn't last forever, maybe 5-10 years if you're lucky. If you want to pry apart the thermostat, then pry out the circuit board, then search for and buy a new battery, then put it all back together the way it was, you can have a working thermostat again for just a couple of bucks. If you don't want to do that, or if you don't figure out why your new thermostat stopped working, you'll need to replace it. Honeywell has taken a product that lasts as long as your house and replaced it with one you'll need to replace again and again. It's a good deal for Honeywell.